8051 Timers / Counters
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The document describes an 8051-based digital clock application that uses timers and interrupts. It configures Timer 0 to generate interrupts every 50ms by overflowing every 46080 cycles. Timer 1 is used to generate a 19200 baud rate for a serial port. On each Timer 0 interrupt, the clock display is updated. By generating interrupts every 50ms and counting 20 of them for 1 second, the timer configuration provides an approximate 1 second timer without exceeding the 8051's 65536 cycle limit.
![Application Example
Digital Clock
DIGITAL CLOCK
VDD
VSS
VEE
RW
RS
D0
D1
D2
D3
D4
D5
D6
D7
E
1
2
3
4
5
6
7
8
9
10
11
12
13
14
mov IE,#10010010b GND
VDD
mov TMOD,#00100001b
RXD
TXD
C1
33p
C2
33p
orl TCON,#00101000b
RTS
CTS
X1
mov
U1
19
XTAL1
SCON,#01110000b
AD[0..7]
11.0592MHz
mov
18
XTAL2 TH1,#0xFD
A[8..15]
30
mov TH1, TL1
ALE
31
EA
9 29
RST PSEN
mov
1
2
P1.0
TL0,#high(TIMER)
P3.0/RXD
10
11
P1.1 P3.1/TXD
3 12
mov TH0,#low(TIMER)
P1.2 P3.2/INT0
4 13
P1.3 P3.3/INT1
5 14
P1.4 P3.4/T0
6 15
P1.5 P3.5/T1
7 16
P1.6 P3.6/WR
8 17
P1.7 P3.7/RD
8051
April 10 48](https://image.slidesharecdn.com/presentation-121208194010-phpapp02/85/8051-Timers-Counters-48-320.jpg)
8051 Timers / Counters
- 1. 8051 Timers / Counters José Borges ,Patrício Lima, Marcos Brito, Marek Mastyło, Jakub Nyk GROUP 4 DEEC –MPIN FEUP April, 2010 April 10
- 2. Outlines 1. Introduction 2. 8051 Timer/Counter 3. Operating Modes 4. Timer Vs Counter 5. T/C and Interruptions 6. Application Examples 7. Conclusion April 10 2
- 3. Introduction General Function: • Calculating the amounts of time between events • Counting events • Generating baud rate for serial port April 10 3
- 4. Introduction Applications: • Communication ̵ Generating rectangular pulses (signal modulation) ̵ Watchdog timers • Manufacturing Industry - Counting objects - Measuring intervals • Etc April 10 4
- 5. Introduction 8051 contains two 16-bits timers • T0 • T1 Two different types of timer: • Interval timer • Counter Maximum value is 65536 Initial state can be set by user April 10 5
- 6. Timer/Counter Special Function Registers Timers/Counters can be operated by user with special function registers T0 and T1 share two SFRs: TMOD and TCON Each timer has also two registers dedicated to itself: TH0/TL0 and TH1/TL1 April 10 6
- 7. Timer/Counter Special Function Registers-TMOD TMOD (Timer Mode Register) is a non-bit- addressable, 8-bit register: Reference: http://fivedots.coe.psu.ac.th/~cj/asm/slides/mcs51/timer2.pdf April 10 7
- 8. Timer/Counter Special Function Registers-TMOD Lower 4 bits are for Timer0 Upper 4 bits are for Timer1 GATE bit is used for choice of internal or external control: • GATE=0 is for internal control, start and stop are controlled by software • GATE=1 is for external control, start and stop are controlled by software and and external source C/T bit decides about timer type: interval timer or counter April 10 8
- 9. Timer/Counter Special Function Registers-TMOD M0 and M1 bits are used to set timer mode (the same for Timer0 and Timer1) 8051 delivers 4 timer modes: M1 M0 Mode Description 0 0 Mode 0 13-bit timer 0 1 Mode 1 16-bit timer 1 0 Mode 2 8-bit auto reload 1 1 Mode 3 Split timer mode April 10 9
- 10. Timer/Counter Special Function Registers-TCON TCON (Timer Control Register) is a bit- addressable, 8-bit register where 4 upper bits are responsible for timers/counters: Reference: http://fivedots.coe.psu.ac.th/~cj/asm/slides/mcs51/timer2.pdf April 10 10
- 11. Timer/Counter Special Function Registers-TCON TR0 and TR1 are set by user to turn on (or turn off) Timer0 or Timer1: • TR=0 – turn off • TR=1 – turn on TF0 and TF1 are Timer Flags informing about overflow (then TF=1 and interrupt could be activate if it’s set, should be cleaned) April 10 11
- 12. Timer/Counter Special Function Registers-TCON Equivalent instructions for TCON: • Timer0: - SETB TR0 = SETB TCON.4 - CLR TR0 = CLR TCON.4 - SETB TF0 = SETB TCON.5 - CLR TF0 = CLR TCON.5 • Timer1 - SETB TR1 = SETB TCON.6 - CLR TR1 = CLR TCON.6 - SETB TF1 = SETB TCON.7 - CLR TF1 = CLR TCON.7 April 10 12
- 13. Timer/Counter Special Function Registers-TL/TH TH0 and TL0 are upper and lower registers of Timer0 TH1 and TL1 are upper and lower registers of Timer1 They help to set initial value of timer/counter April 10 13
- 14. Timer Vs Counter Differences Timer • Counts machine cycles Counters: • Counts events as a result of falling slope of external input signal put on a pin Timer mode and counter mode are relative to machine cycle April 10 14
- 15. Timer Vs Counter Differences Timer • Input from internal system clock Counters: • Show the number of events on registers • External input from T0 input pin (P3.4) for Counter 0 • External input from T1 input pin (P3.5) for Counter 1 • External input from Tx input pin. • We use Tx to denote T0 or T1 April 10 15
- 16. Timer Modes Mode 0 Mode 0 is identical for Timer0 and Timer1 Timers work as 13-bit counters, an interrupt is generated when counter overflows. It takes 8192 input pulses to generate the next interrupt Timers use 8 bits of THi and 5 lower bits of TLi After timer overflows TFi (Timer Flag in TCON) is set, an interrupt occurs Where i=0,1 April 10 16
- 17. Timer Modes Mode 0 Structure of Timer1 in mode 0: Reference: Tomasz Starecki; Mikrokontrolery 8051 w praktyce, Twarda oprawa, 2002. ISBN: 83-910067-4-3, Pic. 3.1 April 10 17
- 18. Timer Modes Mode 1 Similar to mode 0 Timers use 8 bits of THi and 8 bits of TLi Timer is a 16-bit counter, it takes 65536 input pulses to generate the next interrupt Improved capacity April 10 18
- 19. Timer Modes Mode 1 Structure of Timer0 in mode 1: Reference: Tomasz Starecki; Mikrokontrolery 8051 w praktyce, Twarda oprawa, 2002. ISBN: 83-910067-4-3, Pic. 3.1 April 10 19
- 20. Timer Modes Mode 2 Timers are 8-bit auto reload Timer is operated by TLi, when TLi overflows TFi is set TLi is auto reloaded with Thi value when overflows THi is never modified when TLi overflows April 10 20
- 21. Timer Modes Mode 2 Structure of Timer1 in mode 2: Reference: Tomasz Starecki; Mikrokontrolery 8051 w praktyce, Twarda oprawa, 2002. ISBN: 83-910067-4-3, Pic. 3.1 April 10 21
- 22. Timer Modes Mode 3 Split-timer mode Timer1 can be put in other modes Timer0 operates TL0 and TH0 as two separate 8-bit timers/counters TL0 works as a 8-bit timer/counter TH0 is a 8-bit timer which counts machine cycles Timer0 is operated with TF0 and TR0, TF1 and TR1 are not used April 10 22
- 23. Timer Modes Mode 3 Structure of Timer1 in mode 3: Reference: Tomasz Starecki; Mikrokontrolery 8051 w praktyce, Twarda oprawa, 2002. ISBN: 83-910067-4-3, Pic. 3.1 April 10 23
- 24. Timer Modes Example Choose mode 1 for Timer: MOV TMOD,#01H Set the value of TH0 and TL0: MOV TH0,#FFH MOV TL0,#FCH Clear Timer flag and start the timer: CLR TF0 SETB TR0 April 10 24
- 25. Timer Modes Example The 8051 starts to count up by incrementing the TH0-TL0 TH0-TL0= FFFCH,FFFDH,FFFEH,FFFFH,0000H Reference: http://www.iau-neyshabur.ac.ir/nokhodchian/5-timer(part%201).ppt April 10 25
- 26. How does a timer count? Timer/Counter counts up It is incremented by microcontroller • Timer is incremented every machine cycle • Coutner is incremented when event is detected April 10 26
- 27. How does a timer count? A single machine cycle consists of 12 crystal pulses, thus timer will count: 11 059 000 / 12 = 921 583 per second April 10 27
- 28. How does a timer count? Example: How many times will the timer be incremented in 0.05 seconds? 0.05 * 921 583 = 46 079.15 times Accuracy is not perfect April 10 28
- 29. How does a timer count? Timer/Counter counts up It is incremented by microcontroller • Timer is incremented every machine cycle • Coutner is incremented when event is detected April 10 29
- 30. How does a timer count? A single machine cycle consists of 12 crystal pulses, thus timer will count: 11 059 000 / 12 = 921 583 per second April 10 30
- 31. How does a timer count? Example: How many times will the timer be incremented in 0.05 seconds? 0.05 * 921 583 = 46 079.15 times Accuracy is not perfect April 10 31
- 32. Timer/ Counter and Interruptions Timer/ Counter can be configured to start an interruption routine Reference: Philips Semiconductors – Family 8051 April 10 32
- 33. How a timer interruption occurs Some Special Registers are used • ET0 and ET1 from Interruption Enable Register • PT0 and T1 from Interruption Priority Register • TF0 and TF1 from T/C Control Register April 10 April 10 33 33
- 34. How a timer interruption occurs Timer/counter interruption process : • ET bit must be set • TR bit must be set to run the timer • The interruption is initialized when overflow occurs April 10 April 10 34 34
- 35. How a timer interruption occurs In this point the Timer overflow Flag is cleared by hardware Reference: Philips Semiconductors – Family 8051 April 10 35
- 36. Software overflow detection How the overflow can be detected if interruption is not enable? • In some cases ,it’s not necessary to enable an interruption • In this case the overflow is detected by software • A routine is necessary to check constantly the overflow occurrence April 10 36
- 37. Software overflow detection • The overflow occurs when the TF is high • TF must be cleared to by software to turn ON the timer April 10 37
- 38. Software overflow detection Delay routine example without enable interruption: cseg at 0000h jmp main … main: … … setb tr0 acall delay50ms … … delay50ms: mov TL0,#low(46080) mov TH0,#high(46080) clr TF0 jnb TF0,$ ret April 10 38
- 39. Application Example Digital Clock Circuit schematic • Interface with LCD display and serial port. April 10 39
- 40. Application Example Digital Clock Interruption configuration • IE mov IE,#10010010b Or setb EA setb ES setb ET0 April 10 40
- 41. Application Example Digital Clock Interruption configuration • TCON orl TCON,#00101000b Or setb TR0 setb TR1 April 10 41
- 42. Application Example Digital Clock Interruption configuration • TMOD mov TMOD,#00100001b Not bit adressable April 10 42
- 43. Application Example Digital Clock Interruption configuration • SCON mov SCON,#01110000b Or setb SM1 setb SM2 setb REN April 10 43
- 44. Application Example Digital Clock Interruption configuration • Serial port baud rate mov TH1,#0xFD • TH1 = TL1=253 mov TH1, TL1 11.0592𝑀𝐻𝑧 𝑏𝑎𝑢𝑑 𝑟𝑎𝑡𝑒 = 2 ∗ 32 ∗ 12 ∗ 256 − 253 𝑏𝑎𝑢𝑑 𝑟𝑎𝑡𝑒 = 19200 April 10 44
- 45. Application Example Digital Clock Interruption configuration Problem : • 8051 only count up to 65536 us How we count 1 second ? April 10 45
- 46. Application Example Digital Clock Interruption configuration TIMER equ 65536-46080 Solution : mov TL0,#high(TIMER) • Count 20*50ms mov TH0,#low(TIMER) 12 50000𝑢𝑠 = ∗ 𝐶𝑖𝑐𝑙𝑒𝑠 11.0592𝑀ℎ𝑧 𝑐𝑖𝑐𝑙𝑒𝑠 = 46080 April 10 46
- 47. Application Example Digital Clock Interruption configuration mov IE,#10010010b mov TMOD,#00100001b orl TCON,#00101000b mov SCON,#01110000b mov TH1,#0xFD mov TH1, TL1 mov TL0,#high(TIMER) mov TH0,#low(TIMER) April 10 47
- 48. Application Example Digital Clock DIGITAL CLOCK VDD VSS VEE RW RS D0 D1 D2 D3 D4 D5 D6 D7 E 1 2 3 4 5 6 7 8 9 10 11 12 13 14 mov IE,#10010010b GND VDD mov TMOD,#00100001b RXD TXD C1 33p C2 33p orl TCON,#00101000b RTS CTS X1 mov U1 19 XTAL1 SCON,#01110000b AD[0..7] 11.0592MHz mov 18 XTAL2 TH1,#0xFD A[8..15] 30 mov TH1, TL1 ALE 31 EA 9 29 RST PSEN mov 1 2 P1.0 TL0,#high(TIMER) P3.0/RXD 10 11 P1.1 P3.1/TXD 3 12 mov TH0,#low(TIMER) P1.2 P3.2/INT0 4 13 P1.3 P3.3/INT1 5 14 P1.4 P3.4/T0 6 15 P1.5 P3.5/T1 7 16 P1.6 P3.6/WR 8 17 P1.7 P3.7/RD 8051 April 10 48
- 49. Application Example Counter w/ Ext. Enabler +1 0 1 1 0 0 1 0 1 April 10 49
- 50. Application Example Leds equ P1 overflow equ R0 Counter w/ Ext. Enabler cseg at 00h jmp main cseg at 1bh Initialization jmp Timer1 ;Counter/ Timer 1 Int. cseg at 40h Timer1: Counter inc overflow ;Do a Task Leds = TL1 Interrupt TF1 reti main: Return mov IE,#88H ;Enables the Timer1 mov TMOD,#0E0h ;Gate =1, Counter selected, Mode 2 Do a Task mov TH1,#00h ;With 00h it counts 255 times mov TL1,#00h setb TR1 ;Begin to count Led: mov Leds,TL1 ; shows the value with Leds of the actual count jmp Led end April 10 50
- 51. Application Example Digital Clock Reference: • http://www.8052.com/tuttimer.phtml • http://www.8052.com/tutlcd2.php • http://www.8051projects.net/lcd- interfacing/introduction.php • ISIS Proteus - http://www.labcenter.co.uk/download/prodemo_d ownload.cfm#professional • Philips Semiconductors - 80C51 Family April 10 51
- 52. Thank you! April 10 52