SE PAI Unit 5_Serial Port Programming in 8051 microcontroller_Part 2
- 1. 1 Unit 5: 8051 Serial Port Programming Part 2 Subject: Processor Architecture & Interfacing (SPPU, Pune 2015 Course of Information Technology) Class: SEIT Semester: II Prepared By, Ms. K. D. Patil, Assistant Professor Department of Information Technology (NBA accredited) Sanjivani College of Engineering, Kopargaon-423603. Maharashtra, India. (An Autonomous Institute, Affiliated with SPPU, Pune.) NAAC ‘A’ Grade Accredited, ISO 9001:2015 certified
- 2. Contents Prepared By: Ms. K. D. Patil, Dept. of Information Technology, Sanjivani COE, Kopargaon 2 Part 1 Basics of Communication Serial Vs Parallel communication Synchronous Vs Asynchronous communication Data Framing in Asynchronous Serial Communication Baud Rate Part 2 Special Function Registers Operating modes of Serial Communication Doubling Baud Rate in 8051 Part 3 Importance of TI Flag Importance of RI Flag Examples
- 3. Special Function Registers Prepared By: Ms. K. D. Patil, Dept. of Information Technology, Sanjivani COE, Kopargaon 3 SBUF (Serial Buffer) Register Byte addressable SCON (Serial Control) Register Bit addressable PCON (Power Control) Register Byte addressable
- 4. SBUF (Serial Buffer) Register Prepared By: Ms. K. D. Patil, Dept. of Information Technology, Sanjivani COE, Kopargaon 4 Byte Addressable SBUF is an 8-bit register used solely for serial communication For a byte data to be transferred via the TxD line, it must be placed in the SBUF register The moment a byte is written into SBUF, it is framed with the start and stop bits and transferred serially via the TxD line SBUF holds the byte of data when it is received by 8051 RxD line When the bits are received serially via RxD, the 8051 de-frames it by eliminating the stop and start bits, making a byte out of the data received, and then placing it in SBUF Example: MOV SBUF, # ’B’ ; load SBUF=42, ASCII for ‘B’ MOV SBUF, A ; copy accumulator into SBUF MOV A, SBUF ; copy SBUF into accumulator
- 5. SCON (Serial Control) Register Prepared By: Ms. K. D. Patil, Dept. of Information Technology, Sanjivani COE, Kopargaon 5 SCON is an 8-bit register used to program the start bit, stop bit, and data bits of data framing, among other things Bit addressable SM0 SM1 SM2 REN TB0 RB0 TI RI SMO SCON.7 Serial port mode specifier SM1 SCON.6 Serial port mode specifier SM2 SCON.5 Used for Multiprocessor Communication REN SCON.4 Set/cleared by software to enable/disable reception TB8 SCON.3 Not Widely used RB8 SCON.2 Not Widely used TI SCON.1 Transmit interrupt flag. Set by the Hardware at beginning of stop bit mode 1. Cleared by software RI SCON.0 Receive interrupt flag. Set by the Hardware halfway through stop bit mode 1. Cleared by software
- 6. SCON (Serial Control) Register Prepared By: Ms. K. D. Patil, Dept. of Information Technology, Sanjivani COE, Kopargaon 6 SM0 (SCON.7), SM1(SCON.6) They determine the framing of data by specifying the number of bits per character, and the start and stop bits SM0 SM1 Serial Modes 0 0 Serial Mode 0 0 1 Serial Mode 1, 8 Bit data, 1 stop Bit, 1 start bit 1 0 Serial Mode 2 1 1 Serial Mode 3 Note: Only mode 1 is of our Interest
- 7. Serial Modes Prepared By: Ms. K. D. Patil, Dept. of Information Technology, Sanjivani COE, Kopargaon 7 Serial Mode 1 Out of 4, only mode 1 is of our interest Other 3 modes are rarely used Asynchronous (single character at a time) Data framing is of 8 bits, 1 stop bit, 1 start bit which makes it compatible with the COM port of IBM compatible PCs Allows baud rate to be variable and is set by Timer 1 of 8051 For each character, a total of 10 bits are transferred where, First bit is start bit, followed by 8 data bits, and finally 1 stop bit
- 8. Serial Modes Prepared By: Ms. K. D. Patil, Dept. of Information Technology, Sanjivani COE, Kopargaon 8 Serial Mode 0 Synchronous (Transfers block of character at a time) Data transferred on RxD Clock on TxD Clock is fixed at oscillator frequency Serial Mode 2 Asynchronous (single character at a time) Data framing is of 11 bits, 1 stop bit, 1 start bit, 8 data bits (programmable 9 data bits) On transmission TB8 bit of SCON is 9th Bit 9th Bit may be used for Data or Parity Bit Baud rate may be 1/32 or 1/64 of oscillator frequency Serial Mode 3 Same as Serial mode 2 with programmable baud rate
- 9. SCON (Serial Control) Register Prepared By: Ms. K. D. Patil, Dept. of Information Technology, Sanjivani COE, Kopargaon 9 SM2 (SCON.5) This enables the multiprocessing capability of the 8051 For us, SM2 = 0 as 8051 will not be used in multiprocessor environment REN (SCON.4) receive enable When REN = 1 (High), it allows 8051 to receive data on RxD pin When REN = 0 (low), the receiver is disable Can be used to block any serial data reception
- 10. SCON (Serial Control) Register Prepared By: Ms. K. D. Patil, Dept. of Information Technology, Sanjivani COE, Kopargaon 10 TB8 (SCON.3) Transfer Bit Used for Serial modes 2 and 3 For us, TB8 = 0 as we are using Serial Mode 1 for programming RB8 (SCON.2) receive Bit Used for Serial modes 2 and 3 In Serial Mode 1, this bit gets the copy of stop Bit when an 8 bit data is received For us, RB8 = 0
- 11. SCON (Serial Control) Register Prepared By: Ms. K. D. Patil, Dept. of Information Technology, Sanjivani COE, Kopargaon 11 TI (SCON.1) transmit interrupt When 8051 finishes the transfer of 8-bit character It raises TI flag to indicate that it is ready to transfer another byte TI bit is raised at the beginning of the stop bit RI (SCON.0) When 8051 receives data serially via RxD, it gets rid of the start and stop bits and places the byte in SBUF register It raises the RI flag bit to indicate that a byte has been received and should be picked up before it is lost RI is raised halfway through the stop bit
- 12. Doubling Baud Rate in 8051 Prepared By: Ms. K. D. Patil, Dept. of Information Technology, Sanjivani COE, Kopargaon 12 There are two ways to increase the baud rate of data transfer To use a higher frequency crystal This is not feasible as System crystal is fixed New Crystal Frequency may not be compatible with IBM PC serial COM’s port baud rate To change a bit in the PCON register
- 13. PCON (Power Control) Register Prepared By: Ms. K. D. Patil, Dept. of Information Technology, Sanjivani COE, Kopargaon 13 It is an 8-bit register Byte addressable SMOD (Serial mode) bit used serial communication When 8051 is powered up, SMOD is zero We can set it to high by software and the double the baud rate SMOD ---- ---- ---- GF1 GF0 PD IDL D7 D6 D5 D4 D3 D2 D1 D0
- 14. PCON (Power Control) Register Prepared By: Ms. K. D. Patil, Dept. of Information Technology, Sanjivani COE, Kopargaon 14 Following set of sequence can be used to set high D7 of PCON MOV A,PCON ;place a copy of PCON in ACC SETB ACC.7 ;make D7=1 MOV PCON,A ;now SMOD=1 without ;changing any other bits Note: PCON is byte addressable so cannot directly set bit D7 to high
- 15. PCON (Power Control) Register Prepared By: Ms. K. D. Patil, Dept. of Information Technology, Sanjivani COE, Kopargaon 15 GF1 and GF0 Bits Both are general purpose flag bits PD (Power Down) Bit Setting this bit activates Power down operation Available only in CMOS IDL (Idle mode) Bit Setting this bit activates Idle mode operation Available only in CMOS
- 16. Doubling Baud Rate in 8051 Prepared By: Ms. K. D. Patil, Dept. of Information Technology, Sanjivani COE, Kopargaon 16 Considering, XTAL = 11.0592 MHz For SMOD = 0 Machine cycle freq. = 11.0592 MHz / 12 = 921.6 kHz Timer 1 frequency to set Baud Rate = 921.6 kHz / 32 = 28800 Hz For SMOD = 1 Machine cycle freq. = 11.0592 MHz / 12 = 921.6 kHz Timer 1 frequency to set Baud Rate = 921.6 kHz / 16 = 57,600 Hz
- 17. Doubling Baud Rate in 8051 Prepared By: Ms. K. D. Patil, Dept. of Information Technology, Sanjivani COE, Kopargaon 17 Baud Rate Comparison for SMOD = 0 and SMOD = 1 TH1 (Decimal) TH1 (Hex) Baud Rate (SMOD = 0) Baud Rate (SMOD = 1) -3 FD 9600 19200 -6 FA 4800 9600 -12 F4 2400 4800 -24 E8 1200 2400
- 18. Reference Prepared By: Ms. K. D. Patil, Dept. of Information Technology, Sanjivani COE, Kopargaon 18 “The 8051 Microcontroller and Embedded Systems using Assembly and C” , Muhammad Ali Mazidi, Janice Gillispie Mazidi, Rolin D. McKinlay, Second Edition, Pearson publication
- 19. Prepared By: Ms. K. D. Patil, Dept. of Information Technology, Sanjivani COE, Kopargaon 19