27911 gyroscope appnote2

April 2011 Doc ID 018750 Rev 1 1/41
AN3393
Application note
L3G4200D: three axis digital output gyroscope
Introduction
This document is intended to provide usage information and application hints related to ST
L3G4200D 3-axial digital gyroscope.
The L3G4200D is an is three-axis angular rate sensor, with a digital I2
C/SPI serial interface
standard output.
The device has a full scale of ±250/±500/ ±2000 dps and is capable of measuring rates with
a user-selectable bandwidth.
The device may be configured to generate interrupt signals by an independent wake-up
event. Thresholds and timing of the interrupt generator are programmable by the end user
on the fly.
The L3G4200D has an integrated 32-level first in first out (FIFO) buffer allowing the user to
store data for host processor intervention reduction.
The L3G4200D is available in a small thin plastic land grid array package (LGA 4x4x1.1)
and it is guaranteed to operate over an extended temperature range from -40 °C to +85 °C.
The ultra small size and weight of the SMD package make it an ideal choice for handheld
portable applications such as cell phones and PDAs, or any other application where
reduced package size and weight are required.
www.st.com

Contents AN3393
2/41 Doc ID 018750 Rev 1
Contents
1 Registers table . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
2 Operating modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
2.1 Power-down mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
2.2 Sleep mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
2.3 Normal mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
2.4 Switch mode timing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
3 Startup sequence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
3.1 Reading angular rate data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
3.1.1 Using the status register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
3.1.2 Using the data-ready (DRY) signal . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
3.1.3 Using the block data update (BDU) feature . . . . . . . . . . . . . . . . . . . . . . 11
3.2 Understanding angular rate data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
3.2.1 Data alignment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
3.2.2 Big-little endian selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
3.2.3 Example of angular rate data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
4 Digital filters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
4.1 Filters configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
4.2 Low pass filters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
4.3 High Pass filter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
4.3.1 Normal mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
4.3.2 Reference mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
4.3.3 Autoreset . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
5 Interrupt generation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
5.1 Interrupt pin configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
5.2 Interrupt configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
5.3 Threshold . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
5.4 Duration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
5.5 Selective axis movement and wake-up interrupts . . . . . . . . . . . . . . . . . . 22
5.5.1 Wake-up . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

AN3393 Contents
Doc ID 018750 Rev 1 3/41
5.5.2 HP filter bypassed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
5.5.3 Using the HP filter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
5.6 Selective axis movement detection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
6 First in first out (FIFO) buffer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
6.1 FIFO description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
6.2 FIFO registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
6.2.1 Control register 5 (0x24) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
6.2.2 FIFO control register (0x2E) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
6.2.3 FIFO source register (0x2F) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
6.3 FIFO modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
6.3.1 Bypass mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
6.3.2 FIFO mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
6.3.3 Stream mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
6.3.4 Stream-to-FIFO mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
6.3.5 Bypass-to-stream mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
6.4 Watermark . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
6.5 Retrieve data from FIFO . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
7 Temperature sensor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
8 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40

List of tables AN3393
4/41 Doc ID 018750 Rev 1
List of tables
Table 1. Registers table . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Table 2. Operating mode selection. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Table 3. Data rate configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Table 4. Power consumption . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Table 5. Turn-on time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Table 6. Output data registers content vs. angular rate (FS = 250 dps). . . . . . . . . . . . . . . . . . . . . . 12
Table 7. CTRL_REG5 register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Table 8. Out_Sel configuration setting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Table 9. INT_SEL configuration setting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Table 10. Low pass filters cut-off frequency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Table 12. High pass filter cut-off frequency [Hz]. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Table 13. High pass filter mode configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Table 14. Reference mode LSB value . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Table 16. CTRL_REG3 description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
Table 17. INT1_CFG register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
Table 18. INT1_CFG description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
Table 19. Interrupt mode configuration. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
Table 20. INT1_THS_xH register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
Table 21. INT1_THS_xL register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
Table 22. Threshold LSB value . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
Table 23. INT1_DURATION register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
Table 24. INT1_DURATION description. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
Table 25. Duration LSB value in normal mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
Table 26. FIFO buffer full representation (32nd sample set stored) . . . . . . . . . . . . . . . . . . . . . . . . . . 27
Table 27. FIFO overrun representation (33rd sample set stored and 1st sample discarded). . . . . . . 28
Table 28. FIFO enable bit in CTRL_REG5 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
Table 29. FIFO_CTRL_REG . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
Table 30. FIFO_SRC_REG . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
Table 31. FIFO_SRC_REG behavior assuming FTH[4:0] = 15 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
Table 32. CTRL_REG3 (0x22) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
Table 33. Document revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40

AN3393 List of figures
Doc ID 018750 Rev 1 5/41
List of figures
Figure 1. Data ready signal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Figure 2. Low-pass/High-pass filter connections block diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Figure 3. HP_FILTER_RESET readings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Figure 4. Reference mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Figure 5. Autoreset . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Figure 6. Interrupt signals and interrupt pins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
Figure 7. Wait disabled . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
Figure 8. Wait enabled. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
Figure 9. No-move, wake-up interrupt generator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
Figure 10. NM_WU_CFG high and low . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
Figure 11. Wake-up interrupt . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
Figure 12. No-move interrupt . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
Figure 13. FIFO_EN connection block diagram. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
Figure 14. FIFO mode behavior. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
Figure 15. Stream mode fast reading behavior . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
Figure 16. Stream mode slow reading behavior . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
Figure 17. Stream mode slow reading zoom . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
Figure 18. Stream-to-FIFO mode: interrupt not latched. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
Figure 19. Stream-to-FIFO mode: interrupt latched. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
Figure 20. Bypass-to-stream mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
Figure 21. Watermark behavior - FTH[4:0] = 10 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
Figure 22. FIFO reading diagram - FTH[4:0] = 10 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38

AN3393Registerstable
DocID018750Rev16/41
1 Registers table
Table 1. Registers table
Register name Address Bit7 Bit6 Bit5 Bit4 Bit3 Bit2 Bit1 Bit0
WHO_AM_I 0Fh 1 1 0 1 0 0 1 1
CTRL_REG1 20h DR1 DR0 BW1 BW0 PD Zen Yen Xen
CTRL_REG2 21h 0 0 HPM1 HPM0 HPCF3 HPCF2 HPCF1 HPCF0
CTRL_REG3 22h I1_Int1 I1_Boot H_Lactive PP_OD I2_DRDY I2_WTM I2_ORun I2_Empty
CTRL_REG4 23h BDU BLE FS1 FS0 - ST1 ST0 SIM
CTRL_REG5 24h BOOT FIFO_EN -- HPen INT1_Sel1 INT1_Sel0 Out_Sel1 Out_Sel0
REFERENCE 25h REF7 REF6 REF5 REF4 REF3 REF2 REF1 REF0
OUT_TEMP 26h Temp7 Temp6 Temp5 Temp4 Temp3 Temp2 Temp1 Temp0
STATUS_REG 27h ZYXOR ZOR YOR XOR ZYXDA ZDA YDA XDA
OUT_X_L 28h XD7 XD6 XD5 XD4 XD3 XD2 XD1 XD0
OUT_X_H 29h XD15 XD14 XD13 XD12 XD11 XD10 XD9 XD8
OUT_Y_L 2Ah YD7 YD6 YD5 YD4 YD3 YD2 YD1 YD0
OUT_Y_H 2Bh YD15 YD14 YD13 YD12 YD11 YD10 YD9 YD8
OUT_Z_L 2Ch ZD7 ZD6 ZD5 ZD4 ZD3 ZD2 ZD1 ZD0
OUT_Z_H 2Dh ZD15 ZD14 ZD13 ZD12 ZD11 ZD10 ZD9 ZD8
FIFO_CTRL_REG 2Eh FM2 FM1 FM0 WTM4 WTM3 WTM2 WTM1 WTM0
FIFO_SRC_REG 2Fh WTM OVRN EMPTY FSS4 FSS3 FSS2 FSS1 FSS0
INT1_CFG 30h AND/OR LIR ZHIE ZLIE YHIE YLIE XHIE XLIE
INT1_SRC 31h - IA ZH ZL YH YL XH XL
INT1_TSH_XH 32h - THSX14 THSX13 THSX12 THSX11 THSX10 THSX9 THSX8
INT1_TSH_XL 33h THSX7 THSX6 THSX5 THSX4 THSX3 THSX2 THSX1 THSX0
INT1_TSH_YH 34h - THSY14 THSY13 THSY12 THSY11 THSY10 THSY9 THSY8

RegisterstableAN3393
7/41DocID018750Rev1
INT1_TSH_YL 35h THSY7 THSY6 THSY5 THSY4 THSY3 THSY2 THSY1 THSY0
INT1_TSH_ZH 36h - THSZ14 THSZ13 THSZ12 THSZ11 THSZ10 THSZ9 THSZ8
INT1_TSH_Z 37h THSZ7 THSZ6 THSZ5 THSZ4 THSZ3 THSZ2 THSZ1 THSZ0
INT1_DURATION 38h WAIT D6 D5 D4 D3 D2 D1 D0
Table 1. Registers table (continued)
Register name Address Bit7 Bit6 Bit5 Bit4 Bit3 Bit2 Bit1 Bit0

Operating modes AN3393
8/41 Doc ID 018750 Rev 1
2 Operating modes
The L3G4200D provides three different operating modes, respectively reported as power-
down mode, sleep mode and normal mode.
After power supply is applied, the L3G4200D performs a 10 ms boot procedure to load the
trimming parameter. After the boot is completed, the device is automatically configured in
power-down mode.
Referring to the L3G4200D datasheet, output data rate (ODR), power down (PD) and Zen,
Yen, Xen bits of CTRL_REG1 are used to select the operating modes (power-down mode,
low power mode and normal mode) and output data rate (Table 2 and Table 3).
Table 4 shows the typical values of the power consumption for the different operating
modes. Power consumption in normal mode is independent on selected ODR.
Table 2. Operating mode selection
Operating mode PD Zen Yen Xen
Power down 0 - - -
Sleep 1 0 0 0
Normal mode 1 - - -
Table 3. Data rate configuration
DR <1:0> BW <1:0> ODR [Hz] Cut-off LPF1 [Hz] Cut-off LPF2 [Hz]
00 00 100
32
12.5
00 01 100 25
00 10 100 25
00 11 100 25
01 00 200
54
12.5
01 01 200 25
01 10 200 50
01 11 200 70
10 00 400
78
20
10 01 400 25
10 10 400 50
10 11 400 110
11 00 800
93
30
11 01 800 35
11 10 800 50
1 11 800 110

AN3393 Operating modes
Doc ID 018750 Rev 1 9/41
2.1 Power-down mode
When the device is in power-down mode, almost all internal blocks of the device are
switched off to minimize power consumption. Digital interfaces (I2
C and SPI) are still active
to allow communication with the device. The configuration registers content is preserved
and output data registers are not updated, therefore keeping the last data sampled in
memory before going into power-down mode.
2.2 Sleep mode
While the device is in sleep mode the driving circuitry making the moving mass of the
gyroscope oscillating is kept active. Turn-on time from sleep mode to normal mode is
drastically reduced.
2.3 Normal mode
In normal mode, data are generated at the data rate (ODR) selected through the DR bits.
Data interrupt generation is active and configured through the INT1_CFG register.
2.4 Switch mode timing
Switch mode time is shown in Table 5.
Table 4. Power consumption
Operating mode Power consumption
Power-down 5 µA
Sleep 1.5 mA
Normal 6.1 mA
Table 5. Turn-on time
Starting mode Target mode Turn-on time - TYP
Power-down Normal 250 ms
Power-down Self test 250 ms
Sleep Normal
1/ODR: LPF2 disabled
6/ODR: LPF2 enabled
Normal Sleep immediate
Normal Power-down immediate
Other settings change -
1/ODR: LPF2 disabled
6/ODR: LPF2 enabled

Startup sequence AN3393
10/41 Doc ID 018750 Rev 1
3 Startup sequence
Once the device is powered-up, it automatically downloads the calibration coefficients from
the embedded flash to the internal registers. When the boot procedure is completed, i.e.
after approximately 5 milliseconds, the device automatically enters power-down mode. To
turn-on the device and gather angular rate data, it is necessary to select one of the
operating modes through CTRL_REG1 and to enable at least one of the axes.
The following general purpose sequence can be used to configure the device:
3.1 Reading angular rate data
3.1.1 Using the status register
The device is provided with a STATUS_REG which should be polled to check when a new
set of data is available. The reading procedure should be the following:
1. Write CTRL_REG2
2. Write CTRL_REG3
3. Write CTRL_REG4
4. Write CTRL_REG6
5. Write Reference
6. Write INT1_THS
7. Write INT1_DUR
8. Write INT1_CFG
9. Write CTRL_REG5
10. Write CTRL_REG1
1. Read STATUS_REG
2. If STATUS_REG(3) = 0 then go to 1
3. If STATUS_REG(7) = 1 then some data have been overwritten
4. Read OUT_X_L
5. Read OUT_X_H
6. Read OUT_Y_L
7. Read OUT_Y_H
8. Read OUT_Z_L
9. Read OUT_Z_H
10. Data processing
11. Go to 1

AN3393 Startup sequence
Doc ID 018750 Rev 1 11/41
The check performed at step 3 allows to understand whether the reading rate is adequate
compared to the data production rate. In case one or more angular rate samples have been
overwritten by new data, because of a too slow reading rate, the ZYXOR bit of
STATUS_REG is set to 1.
The overrun bits are automatically cleared when all the data present inside the device have
been read and new data have not been produced in the meantime.
3.1.2 Using the data-ready (DRY) signal
The device may be configured to have one HW signal to determinate when a new set of
measurement data is available for reading. This signal is represented by the XYZDA bit of
STATUS_REG. The signal can be driven to DRY/INT2 pin by setting the I2_DRDY bit of
CTRL_REG3 to 1 and its polarity set to active-low or active-high through the H_Lactive bit of
CTRL_REG3 (see Section 5.1).
The data-ready signal rises to 1 when a new set of angular rate data has been generated
and it is available for reading.The interrupt is reset when the higher part of one of the
enabled channels has been read (29h, 2Bh, 2Dh).
Figure 1. Data ready signal
3.1.3 Using the block data update (BDU) feature
If the reading of the angular rate data is particularly slow and cannot be synchronized (or it
is not required) with either the XYZDA bit present inside the STATUS_REG or with the RDY
signal, it is strongly recommended to set the BDU (block data update) bit in CTRL_REG4 to
1.
This feature avoids the reading of values (most significant and least significant parts of the
angular rate data) related to different samples. In particular, when the BDU is activated, the
data registers related to each channel always contain the most recent angular rate data
produced by the device, but, in case the reading of a given pair (i.e. OUT_X_H and
OUT_X_L, OUT_Y_H and OUT_Y_L, OUT_Z_H and OUT_Z_L) is initiated, the refresh for
that pair is blocked until both MSB and LSB parts of the data are read.
Note: BDU only guarantees that OUT_X(Y, Z)_L and OUT_X(Y,Z)_H have been sampled at the
same moment. For example, if the reading speed is too low, it may read X and Y sampled at
T1 and Z sampled at T2.

Startup sequence AN3393
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3.2 Understanding angular rate data
The measured angular rate data are sent to OUT_X_H, OUT_X_L, OUT_Y_H, OUT_Y_L,
OUT_Z_H, and OUT_Z_L registers. These registers contain, respectively, the most
significant part and the least significant part of the angular rate signals acting on the X, Y,
and Z axes.
The complete angular rate data for the X (Y, Z) channel is given by the concatenation
OUT_X_H & OUT_X_L (OUT_Y_H & OUT_Y_L, OUT_Z_H & OUT_Z_L) and it is
expressed as a 2’s complement number.
3.2.1 Data alignment
Angular rate data are represented as 16-bit numbers and are left justified.
3.2.2 Big-little endian selection
The L3G4200D allows to swap the content of the lower and the upper part of the angular
rate registers (i.e. OUT_X_H with OUT_X_L), to be compliant with both little-endian and big-
endian data representations.
“Little Endian” means that the low-order byte of the number is stored in memory at the
lowest address, and the high-order byte at the highest address. (The little end comes first).
This mode corresponds to bit BLE in CTRL_REG4 reset to 0 (default configuration).
On the contrary, “Big Endian” means that the high-order byte of the number is stored in
memory at the lowest address, and the low-order byte at the highest address.
3.2.3 Example of angular rate data
Table 6 provides a few basic examples of the data that is read in the data-registers when the
device is subject to a given angular rate. The values listed in the table are given under the
hypothesis of perfect device calibration (i.e. no offset, no gain error,....) and practically show
the effect of the BLE bit.
Table 6. Output data registers content vs. angular rate (FS = 250 dps)
Angular rate values
BLE = 0 BLE = 1
Register address
28h 29h 28h 29h
0 dps 00h 00h 00h 00h
100 dps A4h 2Ch 2Ch A4h
200 dps 49h 59h 59h 49h
-100 dps 5Ch C4h C3h 5Ch
-200 dps B7h A6h A6h B7h

AN3393 Digital filters
Doc ID 018750 Rev 1 13/41
4 Digital filters
The L3G4200D provides embedded low-pass and as well as high-pass filtering capability to
easily delete the DC component of the measured angular rate. As shown in Figure 2,
through HPen, INTx_Sel and Out_Sel bits of CTRL_REG5 configuration, it is possible to
independently apply the filter on the output/fifo data and/or on the interrupts data. This
means that it is possible, i.e., to get filtered data while interrupt generation works on
unfiltered data.
Figure 2. Low-pass/High-pass filter connections block diagram
4.1 Filters configuration
Referring to Table 8, HPen and Out_sel bits are used to drive unfilterd or filterd data to the
output registers and to the FIFO:
Table 7. CTRL_REG5 register
BOOT FIFO_EN - HPen INT1_Sel1 INT1_Sel0 Out_Sel1 Out_Sel0
Table 8. Out_Sel configuration setting
Hpen OUT_SEL1 OUT_SEL0 Description
x 0 0
Data in DataReg and FIFO are non-high-
pass-filtered
x 0 1
Data in DataReg and FIFO are high-pass-
filtered
0 1 x
Data in DataReg and FIFO are low-pass-
filtered by LPF2
1 1 x
Data in DataReg and FIFO are high-pass and
low-pass-filtered by LPF2

Digital filters AN3393
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Referring to Table 9, HPen and Int_sel bits are used to drive unfilterd or filterd data to the
interrupt generator circuitry:
4.2 Low pass filters
The bandwidth of the low-pass filters depends on the selected ODR. The low-pass filters
cut-off frequencies (ft) are shown in Table 12.
Table 9. INT_SEL configuration setting
Hpen INT_SEL1 INT_SEL2 Description
x 0 0
Non-high-pass-filtered data are used for
interrupt generation
x 0 1
High-pass-filtered data are used for interrupt
generation
0 1 x
Low-pass-filtered data are used for interrupt
generation
1 1 x
High-pass and low-pass-filtered data are
used for interrupt generation
Table 10. Low pass filters cut-off frequency
DR <1:0> BW <1:0> ODR [Hz] Cut-off LPF1 [Hz] Cut-off LPF2 [Hz]
00 00 100
32
12.5
00 01 100 25
00 10 100 25
00 11 100 25
01 00 200
54
12.5
01 01 200 25
01 10 200 50
01 11 200 70
10 00 400
78
20
10 01 400 25
10 10 400 50
10 11 400 110
11 00 800
93
30
11 01 800 35
11 10 800 50
1 11 800 110

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4.3 High Pass filter
The bandwidth of the high-pass filter depends on the selected ODR and on the settings of
HPCFx bits of CTRL_REG2. The high-pass filter cut-off frequencies (ft) are shown in
Table 12.
Referring to Table 13, three operating modes are possible for the high-pass filter:
0(1)
1. Value loaded at boot. This value must not be changed
0(1)
HPM1 HPM1 HPCF3 HPCF2 HPCF1 HPCF0
Table 12. High pass filter cut-off frequency [Hz]
HPCF3-0
ODR [Hz]
100 200 400 800
0000 8 15 30 56
0001 4 8 15 30
0010 2 4 8 15
0011 1 2 4 8
0100 0.5 1 2 4
0101 0.2 0.5 1 2
0110 0.1 0.2 0.5 1
0111 0.05 0.1 0.2 0.5
1000 0.02 0.05 0.1 0.2
1001 0.01 0.02 0.05 0.1
Table 13. High pass filter mode configuration
HPM1 HPM0 High Pass filter Mode
0 0 Normal mode (reset reading REFERENCE register)
0 1 Reference signal for filtering
1 0 Normal mode (reset reading REFERENCE register)
1 1 Autoreset on interrupt event

Digital filters AN3393
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4.3.1 Normal mode
In this configuration the high-pass filter can be reset reading the REFERENCE register,
instantly deleting the DC component of the angular rate.
Figure 3. HP_FILTER_RESET readings
4.3.2 Reference mode
In this configuration the output data is calculated as the difference between the input
angular rate and the content of the reference register. This register is in 2’ complement
representation and the value of 1 LSB of these 8-bit registers depends on the selected full
scale (Table 14).
Table 14. Reference mode LSB value
Full scale Reference mode LSB value (mdps)
250 ~2
500 ~4
2000 ~16

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Figure 4. Reference mode
4.3.3 Autoreset
In this configuration the filter is automatically reset when the configured interrupt event
occurs. HP_RESET is, however, used to set the filter instantaneously.
Note: XYZ dataset used to reset the filter is the one after the interrupt.
Figure 5. Autoreset
AM08454v1
Filtered Data
REFERENCE enable
Input Acceleration

Interrupt generation AN3393
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5 Interrupt generation
The L3G4200D interrupt signal can be configured in a very flexible way allowing to
recognize independent rotations of X,Y and Z axis. That signal can be driven to INT1pin.
INT2 pin is dedicated to DRY and FIFO interrupts.
5.1 Interrupt pin configuration
The device is provided with two pins which can be activated to generate either the data-
ready or the interrupt signals. The functionality of the pins is selected through
CTRL_REG3(22h). Refer to and to the block diagram given in Figure 6.
Figure 6. Interrupt signals and interrupt pins
I1_Int1 I1_Boot H_Lactive PP_OD I2_DRDY I2_WTM I2_ORun I2_Empty
Table 16. CTRL_REG3 description
I1_Int1 Interrupt enable on INT1 pin. Default value 0. (0: Disable; 1: Enable)
I1_Boot Boot status available on INT1. Default value 0. (0: Disable; 1: Enable)
H_Lactive Interrupt active configuration on INT1. Default value 0. (0: High; 1:Low)
PP_OD Push-Pull / Open drain. Default value: 0. (0: Push-Pull; 1: Open drain)
I2_DRDY Date Ready on DRDY/INT2. Default value 0. (0: Disable; 1: Enable)
I2_WTM FIFO Watermark interrupt on DRDY/INT2. Default value: 0. (0: Disable; 1: Enable)
I2_ORun FIFO Overrun interrupt on DRDY/INT2 Default value: 0. (0: Disable; 1: Enable)
I2_Empty FIFO Empty interrupt on DRDY/INT2. Default value: 0. (0: Disable; 1: Enable)

AN3393 Interrupt generation
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5.2 Interrupt configuration
The L3G4200D offers several possibilities to personalize the interrupt signal. The registers
involved in the interrupt generation behavior are INT1_CFG, INT1_THS and
INT1_DURATION.
Whenever an interrupt condition is verified the interrupt signal is generated and by reading
the INT1_SRC register it is possible to understand which condition happened.
Reading INT1_SRC also clears INT1_SRC IA bit (and eventually the interrupt signal on
INT1 pin) and allows the refreshment of data in the INT1_SRC register if the latched option
was chosen.
Table 17. INT1_CFG register
AND/OR LIR ZHIE ZLIE YHIE YLIE XHIE XLIE
Table 18. INT1_CFG description
AND/OR
AND/OR combination of Interrupt events. Default value: 0
(0: OR combination of interrupt events 1: AND combination of interrupt events
LIR
Latch Interrupt Request. Default value: 0
(0: interrupt request not latched; 1: interrupt request latched)
Cleared by reading INT1_SRC reg.
ZHIE
Enable interrupt generation on Z high event. Default value: 0
(0: disable interrupt request; 1: enable interrupt request on measured rate value
higher than preset threshold)
ZLIE
Enable interrupt generation on Z low event. Default value: 0
(0: disable interrupt request; 1: enable interrupt request on measured rate value lower
than preset threshold)
YHIE
Enable interrupt generation on Y high event. Default value: 0
YLIE
Enable interrupt generation on Y low event. Default value: 0
XHIE
Enable interrupt generation on X high event. Default value: 0
XLIE
Enable interrupt generation on X low event. Default value: 0
Table 19. Interrupt mode configuration
AOI Interrupt mode
0 OR combination of interrupt events
1 AND combination of interrupt events

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5.3 Threshold
Threshold registers INT1_THS_xH and INT_THS_xL (respectively MSB and LSB) define
the reference angular rates used by interrupt generation circuitry.
The value of 1 LSB of the threshold depends on the selected full scale (Table 22).
5.4 Duration
The content of the Dx bits of the duration register sets the minimum duration of the interrupt
event to be recognized.
Duration steps and maximum values depend on the ODR chosen.
Duration time is measured in N/ODR, where N is the content of the duration register and
ODR is 100, 200, 400, 800.
Table 20. INT1_THS_xH register
- THSx14 THSx13 THSx12 THSx11 THSx10 THSx9 THSx8
Table 21. INT1_THS_xL register
THSx7 THSx6 THSx5 THSx4 THSx3 THSx2 THSx1 THSx0
Table 22. Threshold LSB value
Full scale Threshold LSB value (mdps)
100 ~3
200 ~6.1
400 ~12.2
800 ~24.5
Table 23. INT1_DURATION register
WAIT D6 D5 D4 D3 D2 D1 D0
Table 24. INT1_DURATION description
WAIT WAIT enable. Default value: 0 (0: disable; 1: enable)
D6 - D0 Duration value. Default value: 000 0000
Table 25. Duration LSB value in normal mode
ODR (Hz) Duration LSB value (ms)
100 10
200 5
400 2.5
800 1.25

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WAIT bit of INT1_DURATION register has the following meaning:
Wait =’0’: the interrupt falls immediately if signal crosses the selected threshold (Figure 7)
Wait =’1’: if signal crosses the selected threshold, the interrupt falls only after the duration
has counted number of samples at the selected data rate, written into the duration counter
register (Figure 8).
Figure 7. Wait disabled
Figure 8. Wait enabled

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5.5 Selective axis movement and wake-up interrupts
The L3G4200D interrupts signal can behave as selective axis movement detection and
wake-up. Whenever an interrupt condition is verified, the interrupt signal is generated and by
reading the INT1_SRC register it is possible to understand which condition happened.
The selective axis movement detection signal (SA) and wake-up signal (WU) interrupt
generation block is represented in Figure 9.
The SA or WU interrupt generation is selected through the AOI bit in the INT1_CFG register.
If the AOI bit is ‘0’, signals coming from comparators for the axis enabled through the
INT1_CFG register are put in logical OR. In this case, interrupt is generated when at least
one of the enabled axes exceeds the threshold written in module in INT1_THS_xH and
INT1_THS_xL registers. Otherwise, if the AOI bit is ‘1’, signals coming from comparators
enter a “NAND” port. In this case an interrupt signal is generated only if all the enabled axes
are passing the threshold.
LIR bit of INT1_CFG allows to decide if the interrupt request must be latched or not. If LIR
bit is ‘0’ (default value), the interrupt signal goes high when the interrupt condition is satisfied
and returns to low immediately if the interrupt condition is no longer verified. Otherwise, if
the LIR bit is ‘1’, whenever an interrupt condition is applied the interrupt signal remains high
even if the condition returns to a non-interrupt status until a reading to the INT1_SRC
register is performed.
The ZHIE, ZLIE, YHIE, YLIE, XHIE, and HLIE bits of the INT1_CFG register allow to decide
on which axis the interrupt decision must be performed and on which direction the threshold
must be passed to generate the interrupt request.
Figure 9. No-move, wake-up interrupt generator

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The threshold module which is used by the system to detect any no-move or wake-up event
is defined by the INT1_THS register. The threshold value is expressed over 7 bits as an
unsigned number and is symmetrical around the zero-g level. XH (YH, ZH) is true when the
unsigned angular rate value of the X (Y, Z) channel is higher than INT1_THS. Similarly, XL
(YL, ZL) low is true when the unsigned angular rate value of the X (Y, Z) channel is lower
than INT1_THS. Refer to Figure 10 for more details.
Figure 10. NM_WU_CFG high and low
5.5.1 Wake-up
Wake-up interrupt refers to a specific configuration of the INT1_CTRL register that allows
interrupt generation when the angular rate on the configured axis exceeds a defined
threshold (Figure 11).
Figure 11. Wake-up interrupt

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5.5.2 HP filter bypassed
This paragraph provides a basic algorithm which shows the practical use of the wake-up
feature. In particular, with the code below, the device is configured to recognize when the
absolute angular rate along either the X axis exceeds a preset threshold (100 dps used in
the example). The event which triggers the interrupt is latched inside the device and its
occurrence is signalled through the use of the INT1 pin.
5.5.3 Using the HP filter
The code provided below gives a basic routine which shows the practical use of the wake-up
feature performed on high-pass filtered data. In particular the device is configured to
recognize when the high-frequency component of the angular rate applied along either the
X, Y, or Z axis exceeds a preset threshold (100 dps used in the example).
The event which triggers the interrupt is latched inside the device and its occurrence is
signalled through the use of the INT1 pin.
1 Write 0Fh into CTRL_REG1
// Turn-on the sensor and enable X, Y, and Z
// ODR = 100 Hz
2 Write 00h into CTRL_REG2 // High-pass filter disabled
3 Write 80h into CTRL_REG3 // Interrupt driven to INT1 pad
4 Write 00h into CTRL_REG4 // FS = 250 dps
5 Write 2Ch into INT1_THS_XH // Threshold = 100 dps
6 Write A4h into INT1_THS_XL // Threshold = 100 dps
7 Write 00h into INT1_DURATION // Duration = 0
8 Write 02h into INT1_CFG // Enable XH interrupt generation
9 Poll INT1 pad; if INT1=0 then go to 8
// Poll INT1 pin waiting for the
// wake-up event
10 Read INT1_SRC
// Return the event that has triggered the
// interrupt
11
(Wake-up event has occurred; insert
your code here)
// Event handling
12 Go to 8
// ODR = 100 Hz
2 Write 00h into CTRL_REG2 // High-pass filter in normal mode
5 Write 05h into CTRL_REG5
// Data in DataReg and FIFO are high-pass filtered
// High-pass-filtered data are used for interrupt
// generation

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At step 13, a dummy reading at the REFERENCE register is performed to set the
current/reference angular rate/tilt state against which the device performed the threshold
comparison.
This reading may be performed any time it is required to set current rate as a reference state
without waiting for the filter to settle.
5.6 Selective axis movement detection
Selective axis movement detection refers to a specific configuration of INT1_CTRL register
that allows to recognize when the device is rotating only around the selected axes.
Referring to Figure 12, a “no rotation zone” is defined around the zero-dps level where the
angular rates are small enough to be considered as zero. It is possible to create a
configuration of INT1_CFG register so that an interrupt is generated only if, i.e., angular rate
for rotation around x and y axes are around zero while it is different from zero for z axis. This
means the device is doing a pure yaw rotation.
8 Write 2Ch into INT1_THS_YH // Threshold = 100 dps
9 Write A4h into INT1_THS_YL // Threshold = 100 dps
10 Write 2Ch into INT1_THS_ZH // Threshold = 100 dps
11 Write A4h into INT1_THS_ZL // Threshold = 100 dps
12 Write 00h into INT1_DURATION // Duration = 0
13 Read REFERENCE
// Dummy read to force the HP filter to
// current angular rate value
// (i.e. set reference angular rate)
14 Write 6Ah into INT1_CFG
// Enable XH, YH and ZH interrupt generation
// Interrupt latched
// wake-up event
16 Read INT1_SRC
// interrupt
17
your code here)
// Event handling
18 Go to 15

26/41 Doc ID 018750 Rev 1
Figure 12. No-move interrupt
This paragraph provides the basics for the use of the selective axis movement detection
feature. Here below is reported the example code which implements the SW routine for the
selective axis movement recognition:
The code sample exploits a threshold set at 60 dps selective axis movement detection and
the event is notified by the hardware signal INT1. At step 7, the INT1_DURATION register is
configured like this to ignore events that are shorter than 1/DR = 1/100 ~= 10 msec in order
to avoid false detections. Once the selective axis movement detection has occurred, a
reading of the INT1_SRC register clears the request and the device is ready to recognize
other events.
// ODR = 100 Hz
8 Write 2Ch into INT1_THS_YH // Threshold = 60 dps
9 Write A4h into INT1_THS_YL // Threshold = 60 dps
10 Write 2Ch into INT1_THS_ZH // Threshold = 60 dps
11 Write A4h into INT1_THS_ZL // Threshold = 60 dps
12 Write 01h into INT1_DURATION // Duration = 10 ms
13 Write 65h into INT1_CFG
// Enable XL, YL and ZH interrupt generation in AND
// configuration. Interrupt latched
// wake-up event
15 Read INT1_SRC
// interrupt
16
your code here)
// Event handling
17 Go to 15

AN3393 First in first out (FIFO) buffer
Doc ID 018750 Rev 1 27/41
6 First in first out (FIFO) buffer
In order to decrease the host processor interaction and facilitate post processing data for
events recognition, L3G4200D embeds a first in first out buffer (FIFO) for each of the three
output channels, X, Y, and Z.
FIFO use allows a consistent power saving for the system, it can wake-up only when
needed and burst the significant data out from the FIFO.
The FIFO buffer can work according to four different modes that guarantee a high-level of
flexibility during application development: Bypass mode, FIFO mode, Stream mode, and
Stream-to-FIFO mode.
The programmable watermark level and FIFO overrun event can be enabled to generate
dedicated interrupts on the DRDY/INT2 pin.
6.1 FIFO description
The FIFO buffer is able to store up to 32 angular rate samples of 16 bits for each channel;
data are stored in the 16-bit 2’s complement left justified representation.
The data samples set consists of 6 bytes (Xl, Xh, Yl, Yh, Zl, and Zh) and they are released
to the FIFO at the selected output data rate (ODR).
The new sample set is placed in the first empty FIFO slot until the buffer is full, therefore, the
oldest value is overwritten.
Table 26. FIFO buffer full representation (32nd
sample set stored)
Output
registers
0x28h 0x29h 0x2Ah 0x2Bh 0x2Ch 0x2Dh
Xl(0) Xh(0) Yl(0) Yh(0) Zl(0) Zh(0)
FIFO index FIFO sample set
FIFO(0) Xl(0) Xh(0) Yl(0) Yh(0) Zl(0) Zh(0)
... ... ... ... ... ... ...
... ... ... ... ... ... ...

First in first out (FIFO) buffer AN3393
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Table 26 represents the FIFO full status when 32 samples are stored in the buffer while
Table 27 represents the next step when the 33rd
sample is inserted into FIFO and the 1st
sample is overwritten. The new oldest sample set is made available in the output registers.
When FIFO is enabled and mode is different from bypass, the L3G4200D output registers
(28h to 2Dh) always contain the oldest FIFO sample set.
6.2 FIFO registers
The FIFO buffer is managed by three different accelerometer registers, two of these allow to
enable and configure the FIFO behavior, the third provides information about the buffer
status.
6.2.1 Control register 5 (0x24)
The FIFO_EN bit in CTRL_REG5 must be set to 1 in order to enable the internal first in first
out buffer; while this bit is set, the gyroscope output registers (28h to 2Dh) don’t contain the
current angular rate value but they always contain the oldest value stored in FIFO.
Table 27. FIFO overrun representation (33rd
sample set stored and 1st
sample
discarded)
Output
registers
0x28h 0x29h 0x2Ah 0x2Bh 0x2Ch 0x2Dh
Xl(1) Xh(1) Yl(1) Yh(1) Zl(1) Zh(1)
FIFO index Sample set
... ... ... ... ... ... ...
... ... ... ... ... ... ...
Table 28. FIFO enable bit in CTRL_REG5
b7 b6 b5 b4 b3 b2 b1 b0
X FIFO_EN X X X X X X

Doc ID 018750 Rev 1 29/41
Figure 13. FIFO_EN connection block diagram
6.2.2 FIFO control register (0x2E)
This register is dedicated to FIFO mode selection and watermark configuration.
FM[1:0] bits are dedicated to define the FIFO buffer behavior selection:
1. FM[2:0] = (0,0,0): Bypass mode
2. FM[2:0] = (0,0,1): FIFO mode
3. FM[2:0] = (0,1,0): Stream mode
4. FM[2:0] = (0,1,1): Stream to FIFO mode
5. FM[2:0] = (1,0,0): Bypass-to-FIFO mode
The trigger used to activate stream-to-FIFO and bypass-to-stream modes is related to the IA
bit value of the selected INT1_SRC register and does not depend on the interrupt pin value
and polarity. The trigger is generated also if the selected interrupt is not driven to an
interrupt pin.
WTM[4:0] bits are intended to define the watermark level; when FIFO content exceeds this
value the WTM bit is set to “1” in the FIFO source register.
Table 29. FIFO_CTRL_REG
b7 b6 b5 b4 b3 b2 b1 b0
FM2 FM1 FM0 WTM4 WTM3 WTM2 WTM1 WTM0

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6.2.3 FIFO source register (0x2F)
This register is updated at every ODR and provides information about the FIFO buffer
status.
● WTM bit is set high when FIFO content exceeds watermark level.
● OVRN bit is set high when FIFO buffer is full, this means that the FIFO buffer contains
32 unread samples. At the following ODR a new sample set replaces the oldest FIFO
value. The OVRN bit is reset when the first sample set has been read.
● EMPTY flag is set high when all FIFO samples have been read and FIFO is empty.
● FSS[4:0] field always contains the current number of unread samples stored in the
FIFO buffer. When FIFO is enabled, this value increases at ODR frequency until the
buffer is full, whereas, it decreases every time that one sample set is retrieved from
FIFO.
Register content is updated synchronous to the FIFO write and read operation.
The watermark flag, the FIFO overrun and FIFO empty event can be enabled to generate a
dedicated interrupt on the DRY/INT2 pin by configuring CTRL_REG3.
● I2_WTM bit drives watermark flag (WTM) on the DRY/INT2 pin.
● I2_OVRN bit drives overrun event (OVRN) on the DRY/INT2Y pin.
● I2_Empty bit drives empty event (EMPTY) on the DRY/INT2 pin
Table 30. FIFO_SRC_REG
b7 b6 b5 b4 b3 b2 b1 b0
WTM OVRN EMPTY FSS4 FSS3 FSS2 FSS1 FSS0
Table 31. FIFO_SRC_REG behavior assuming FTH[4:0] = 15
WTM OVRN EMPTY FSS[4:1] Unread FIFO samples Timing
0 0 1 00000 0 t0
0 0 0 00001 1 t0 + 1/ODR
0 0 0 00010 2 t0 + 2/ODR
... ... ... ... ... ...
0 0 0 01111 15 t0 + 15/ODR
1 0 0 10000 16 t0 + 16/ODR
... ... ... ... ... ...
1 0 0 11110 30 t0 + 30/ODR
1 0 0 11111 31 t0 + 31/ODR
1 1 0 11111 32 t0 + 32/ODR
Table 32. CTRL_REG3 (0x22)
b7 b6 b5 b4 b3 b2 b1 b0
X X X X X I2_WTM I2_ORun I2_Empty

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If one ore more bits are set to “1”, the DRY/INT2 pin status is the logical OR combination of
the three signals.
6.3 FIFO modes
The L3G4200D FIFO buffer can be configured to operate in five different modes selectable
by the FM[2:0] field in FIFO_CTRL_REG. Available configurations ensure a high-level of
flexibility and extend the number of functions usable in application development.
Bypass, FIFO, Stream, Stream-to-FIFO and Bypass-to-stream modes are described in the
following paragraphs.
6.3.1 Bypass mode
When bypass mode is enabled, FIFO is not operational: buffer content is cleared, output
registers (0x28 to 0x2D) are frozen at the last value loaded, and the FIFO buffer remains
empty until another mode is selected.
Follow these steps for bypass mode configuration:
1. Turn-on FIFO by setting the FIFO_En bit to “1” in control register 5 (0x24). After this
operation the FIFO buffer is enabled but isn’t collecting data, output registers are frozen
to the last samples set loaded.
2. Activate bypass mode by setting the FN[2:0] field to “000” in the FIFO control register
(0x2E). If this mode is enabled, FIFO source register (0x2F) is forced equal to 0x20.
Bypass mode must be used in order to stop and reset the FIFO buffer when a different mode
is operating. Note that placing the FIFO buffer into bypass mode clears the whole buffer
content.
6.3.2 FIFO mode
In FIFO mode, the buffer continues filling until full (32 sample set stored,) then it stops
collecting data and the FIFO content remains unchanged until a different mode is selected.
Follow these steps for FIFO mode configuration:
2. Activate FIFO mode by setting the FN[2:0] field to “001” in the FIFO control register
(0x2E).
By selecting this mode, FIFO starts data collection and source register (0x2F) changes
according to the number of samples stored. At the end of the procedure, the source register
is set to 0xDF and the OVRN flag generates an interrupt if the I2_OVRN bit is selected in
control register 5. Data can be retrieved when OVRN is set to”1”, performing a 32 sample
set reading from the output registers, data can be retrieved also on the WTM flag instead of
OVRN if the application requires a lower number of samples. Communication speed is not
so important in FIFO mode because data collection is stopped and there is no risk of
overwriting acquired data. Before restarting FIFO mode, at the end of the reading procedure
it is necessary to transit from bypass mode.

32/41 Doc ID 018750 Rev 1
A FIFO mode application hint is reported below:
1. Set FIFO_En = 1: Enable FIFO
2. Set FN[2:0] = (0,0,1): Enable FIFO mode
3. Wait OVRN or WTM interrupt
4. Read data from gyroscope output registers
5. Set FN[2:0] = (0,0,0): Enable bypass mode
6. Repeat from point 2
Figure 14. FIFO mode behavior
If FIFO mode is enabled, the buffer starts to collect data and fill all the 32 slots (from F0 to
F31) at the selected output data rate. When the buffer is full, the OVRN bit goes up and data
collection is permanently stopped; the user can decide to read FIFO content at any time
because it is maintained unchanged until bypass mode is selected. The reading procedure
is composed of a 32 sample set of 6 bytes for a total of 192 bytes and retrieves data starting
from the oldest sample stored in FIFO (F0). The OVRN bit is reset when the first sample set
has been read. The bypass mode setting resets FIFO and allows the user to enable FIFO
mode again.
6.3.3 Stream mode
In stream mode FIFO continues filling, when the buffer is full, the FIFO index restarts from
the beginning and older data is replaced by the current. The oldest values continue to be
overwritten until a read operation makes free FIFO slots available. Host processor reading
speed is most important in order to free slots faster than new data is made available.
FM[2:0] bypass configuration is used to stop this mode.
Follow these steps for FIFO mode configuration:
2. Activate stream mode by setting the FN[2:0] field to “011” in the FIFO control register
(0x2E).

Doc ID 018750 Rev 1 33/41
As described, for FIFO mode, data can be retrieved when OVRN is set to”1” performing a 32
sample set reading from output registers, data can be retrieved also on the WTM flag if the
application requires a smaller number of samples.
Figure 15. Stream mode fast reading behavior
In stream mode, the FIFO buffer is continuously filling (from F0 to F31) at the selected
output data rate. When the buffer is full the OVRN flag goes up and the suggested solution
is to read all FIFO samples (192 bytes) faster then 1*ODR, in order to make free FIFO slots
available for the new angular rate samples. This allows to avoid loss of data and to decrease
the host processor interaction increasing system efficiency. If the reading procedure is not
fast enough, three different cases can be observed:
1. FIFO sample set (6 bytes) reading faster than 1*ODR: data are correctly retrieved
because a free slot is made available before new data is generated.
2. FIFO sample set (6 bytes) reading synchronous to 1*ODR: data are correctly retrieved
because a free slot is made available before new data is generated but FIFO benefits
are not exploited. This case is equivalent to read data on data ready interrupt and does
not reduce the host processor interaction compared to the standard accelerometer
reading.
3. FIFO sample set (6 bytes) reading slower than 1*ODR: in this case some data is lost
because data recovery is not fast enough to free slots for new angular rate data
Figure 16. The number of correctly recovered samples is related to the difference
between the current ODR and the FIFO sample set reading rate.

34/41 Doc ID 018750 Rev 1
Figure 16. Stream mode slow reading behavior
In Figure 16, due to slow reading, data from “jj” are not retrieved because they are replaced
by the new gyroscope samples generated by the system.
Figure 17. Stream mode slow reading zoom
After stream mode enable, FIFO slots are filled at the end of each ODR time frame. The
reading procedure must start as soon as the OVRN flag is set to “1”, data are retrieved from
FIFO at the beginning of the reading operation. When a read command is sent to the device,
the output registers content is moved to the SPI/I2
C register and the current oldest FIFO
value is shifted into the output registers in order to allow the next read operation. In the case
of a reading slower than 1*ODR, some data can be retrieved from FIFO after that new
sample is inserted into the addressed location. In Figure 17 the fourth read command starts
after the refresh of the F3 index and this generates a disconnect in the reading data. The
OVRN flag advises the user that this event has taken place. In this example, three correct
samples have been read, the number of correctly recovered samples is dependent on the
difference between the current ODR and the FIFO sample set reading timeframe.

Doc ID 018750 Rev 1 35/41
6.3.4 Stream-to-FIFO mode
This mode is a combination of the stream and FIFO modes described above. In stream-to-
FIFO mode, the FIFO buffer starts operating in stream mode and switches to FIFO mode
when the selected interrupt occurs.
Follow these steps for stream-to-FIFO mode configuration:
1. Configure desired interrupt generator using register INT1_CFG (0x30).
3. Activate stream-to-FIFO mode by setting the FN[2:0] field to “011” in the FIFO control
register (0x2E).
The interrupt trigger is related to the IA bit in the INT1_SRC register and it is generated even
if the interrupt signal is not driven to an interrupt pad. Mode switch is performed if both IA
and OVRN bits are set high. Stream-to-FIFO mode is sensitive to the trigger level and not to
the trigger edge, this means that if stream-to-FIFO is in FIFO mode and the interrupt
condition disappears, the FIFO buffer returns to stream mode because the IA bit becomes
zero. It is suggested to latch the interrupt signal used as the FIFO trigger in order to avoid
losing interrupt events. If the selected interrupt is latched, it is needed to read the register
INT1_SRC to clear the IA bit; after reading, the IA bit takes 2*ODR to go low.
In stream mode the FIFO buffer continues filling, when the buffer is full, the OVRN bit is set
high and the next samples overwrite the oldest. When trigger occurs, two different cases
can be observed:
1. If the FIFO buffer is already full (OVRN = “1”), it stops collecting data at the first sample
after trigger. FIFO content is composed of #30 samples collected before the trigger
event, the sample that has generated the interrupt event and one sample after trigger.
2. If FIFO isn’t yet full (initial transient), it continues filling until it is full (OVRN = “1”) and
then, if trigger is still present, it stops collecting data.
Figure 18. Stream-to-FIFO mode: interrupt not latched

36/41 Doc ID 018750 Rev 1
Figure 19. Stream-to-FIFO mode: interrupt latched
Stream-to-FIFO can be used in order to analyze the samples history that generate an
interrupt; the standard operation is to read FIFO content when FIFO mode is triggered and
FIFO buffer is full and stopped.
6.3.5 Bypass-to-stream mode
This mode is a combination of the bypass and stream modes described above. In bypass-
to-stream mode, the FIFO buffer starts operating in bypass mode and switches to stream
mode when the selected interrupt occurs.
Follow these steps for bypass-to-stream mode configuration:
1. Configure desired interrupt generator using register INT1_CFG (0x30).
3. Activate bypass-to-stream mode by setting the FN[2:0] field to “100” in the FIFO control
register (0x2E).
The interrupt trigger is related to the IA bit in the INT1_SRC register and it is generated even
if the interrupt signal is not driven to an interrupt pad. Bypass-to-stream mode is sensitive to
the trigger level and not to the trigger edge, this means that if bypass-to-stream is in stream
mode and the interrupt condition disappears, the FIFO buffer returns to bypass mode
because the IA bit becomes zero.
It is suggested to latch the interrupt signal used as the stream trigger in order to avoid losing
interrupt events. If the selected interrupt is latched, it is needed to read the register
INT1_SRC to clear the IA bit; after reading, the IA bit takes 2*ODR to go low.
In stream mode the FIFO buffer continues filling. When the buffer is full, the OVRN bit is set
high and the next samples overwrite the oldest.

Doc ID 018750 Rev 1 37/41
Figure 20. Bypass-to-stream mode
Bypass-to-stream can be used in order to start the acquisition when the configured interrupt
is generated.
6.4 Watermark
Watermark is a configurable flag that can be used to generate specific interrupt in order to
know when the FIFO buffer contains at least the number of samples defined as the
watermark level. The user can select the desired level in a range from 0 to 31 using the
WTM[4:0] field in the FIFO control register while the FIFO source register FSS[4:0] always
contains the number of samples stored in FIFO. If FSS[4:0] is greater than WTM[4:0], the
WTM bit is set high in the FIFO source register, on the contrary, WTM is driven low when the
FSS[4:0] field becomes lower than WTM[4:0]. FSS[4:0] increases by one step at the ODR
frequency and decreases by one step every time that a sample set reading is performed by
the user.
Figure 21. Watermark behavior - FTH[4:0] = 10
In Figure 21, the first row indicates the FSS[4:0] value, the second row indicates the relative
FIFO slot and last row shows the incremental FIFO data. Assuming WTM[4:0] = 10, the
WTM flag changes from “0” to “1” when the eleventh FIFO slot is filled (F10). Figure 22
shows that the WTM flag goes down when the FIFO content is less than WTM[4:0], it means
that nine unread sample sets remain in FIFO.

38/41 Doc ID 018750 Rev 1
The watermark flag (WTM) can be enabled to generate a dedicated interrupt on the
DRY/INT2 pin by setting the I2_WTM bit high in CTRL_REG3.
6.5 Retrieve data from FIFO
When FIFO is enabled and the mode is different to bypass, reading output registers (28h to
2Dh) return the oldest FIFO sample set.
Whenever output registers are read, their content is moved to the SPI/I2C output buffer.
FIFO slots are ideally shifted up one level in order to release room for a new sample
reception and output registers load the current oldest value stored in the FIFO buffer.
The whole FIFO content is retrieved performing thirty two read operations from gyroscope
output registers, every other reading operation returns the same last value until a new
sample set is available in the FIFO buffer.
Data can be retrieved from FIFO using every reading byte combination in order to increase
the application flexibility (ex: 196 single byte reading, 32 reading of 6 bytes, 1 multiple
reading of 196 bytes, etc.).
It is suggested to read all FIFO slots in a multiple byte reading of 196 bytes (6 output
registers by 32 slots) faster than 1*ODR. In order to minimize communication between
master and slave the reading address is automatically updated by the device; it rolls back to
0x28 when register 0x2D is reached.
In order to avoid losing data, the right ODR must be selected according to the serial
communication rate available. In the case of standard I2C mode being used (max rate 100
kHz), a single sample set reading takes 830 µs while total FIFO download is about 17.57ms.
I2C speed is lower than SPI and it needs about 29 clock pulses to start communication
(start, slave address, device address+write, restart, device address+read) plus an additional
9 clock pulses for every byte to read. If this suggestion were followed, the complete FIFO
reading would be performed faster than 1*ODR, this means that using a standard I2C, the
selectable ODR must be lower than 57 Hz. If a fast I2C mode is used (max rate 400 kHz),
the selectable ODR must be lower than 228 Hz.
Figure 22. FIFO reading diagram - FTH[4:0] = 10
In Figure 22 “Rx” indicates a 6-byte reading operation and “F0*” represents a single ODR
slot stretched for diagram convenience.

AN3393 Temperature sensor
Doc ID 018750 Rev 1 39/41
7 Temperature sensor
The L3G4200D is provided with an internal temperature sensor that is suitable for delta
temperature measurement. Temperature data are generated with a frequency of 1 Hz and
are stored inside the OUT_TEMP register in two’s complement format, with a sensitivity if -1
LSB/°C.

Revision history AN3393
40/41 Doc ID 018750 Rev 1
8 Revision history
Table 33. Document revision history
Date Revision Changes
29-Apr-2011 1 Initial release.

AN3393
Doc ID 018750 Rev 1 41/41
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