SE PAI Unit 5_Serial Port Programming in 8051 micro controller_Part 3
- 1. 1 Unit 5: 8051 Serial Port Programming (Part 3) 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. Importance of TI flag Prepared By: Ms. K. D. Patil, Dept. of Information Technology, Sanjivani COE, Kopargaon 3 The steps that 8051 goes through in transmitting a character via TxD The byte character to be transmitted is written into the SBUF register The start bit is transferred The 8-bit character is transferred on bit at a time The stop bit is transferred. It is during the transfer of the stop bit that 8051 raises the TI flag, indicating that the last character was transmitted By monitoring the TI flag, we make sure that we are not overloading the SBUF. If we write another byte into the SBUF before TI is raised, the un-transmitted portion of the previous byte will be lost After SBUF is loaded with a new byte, the TI flag bit must be forced to 0 by CLR TI in order to transfer new byte
- 4. Importance of TI flag Prepared By: Ms. K. D. Patil, Dept. of Information Technology, Sanjivani COE, Kopargaon 4 By checking the TI flag bit, we know whether or not the 8051 is ready to transfer another byte It must be noted that TI flag bit is raised by 8051 itself when it finishes data transfer It must be cleared by the programmer with instruction CLR TI If we write a byte into SBUF before the TI flag bit is raised, we risk the loss of a portion of the byte being transferred The TI bit can be checked by The instruction JNB TI,xx Using an interrupt
- 5. Programming 8051 to transfer character byte Serially Prepared By: Ms. K. D. Patil, Dept. of Information Technology, Sanjivani COE, Kopargaon 5 1. TMOD register is loaded with the value 20H, indicating the use of timer 1 in mode 2 (8-bit auto-reload) to set baud rate 2. The TH1 is loaded with one of the values to set baud rate for serial data transfer 3. The SCON register is loaded with the value 50H, indicating serial mode 1, where an 8-bit data is framed with start and stop bits 4. TR1 is set to 1 to start timer 1 5. TI is cleared by CLR TI instruction 6. The character byte to be transferred serially is written into SBUF register 7. The TI flag bit is monitored with the use of instruction JNB TI, xx to see if the character has been transferred completely 8. To transfer the next byte, go to step 5
- 6. Example No. 1 6 Write 8051 ALP to transfer letter “A” serially at 4800 baud, continuously. Solution: MOV TMOD,#20H ;timer 1,mode 2(auto reload) MOV TH1,#-6 ;4800 baud rate MOV SCON,#50H ;8-bit, 1 stop, REN enabled SETB TR1 ;start timer 1 AGAIN: MOV SBUF,#”A” ;letter “A” to transfer HERE: JNB TI, HERE ;wait for the last bit CLR TI ;clear TI for next char SJMP AGAIN ;keep sending A SM0 SM1 SM2 REN TB0 RB0 TI RI SCON GATE C/T M1 M0 GATE C/T M1 M0 TMOD
- 7. Example No. 2 7 Write a program for the 8051 to transfer “YE” serially at 9600 baud, 8-bit data, 1 stop bit, do this continuously Solution: MOV TMOD,#20H ;timer 1,mode 2(auto reload) MOV TH1,#-3 ;9600 baud rate MOV SCON,#50H ;8-bit, 1 stop, REN enabled SETB TR1 ;start timer 1 AGAIN: MOV A,#”Y” ;transfer “Y” ACALL LOOP MOV A,#”E” ;transfer “E” ACALL LOOP SJMP AGAIN ;keep doing it LOOP: MOV SBUF,A ;load SBUF serial data transfer subroutine HERE: JNB TI,HERE ;wait for the last bit CLR TI ;get ready for next byte RET
- 8. Example No. 3 Prepared By: Ms. K. D. Patil, Dept. of Information Technology, Sanjivani COE, Kopargaon 8 Write 8051 ALP to transfer letter “Y” serially at 9600 baud, continuously, also send a letter “N” through Port 0 which is connected to display device Solution: MOV TMOD,#20H ;timer 1,mode 2(auto reload) MOV TH1,#-3 ;9600 baud rate MOV SCON,#50H ;8-bit, 1 stop, REN enabled SETB TR1 ;start timer 1 AGAIN: MOV SBUF, #”Y” ;transfer “Y” serially HERE: JNB TI,HERE ;wait for the last bit CLR TI ;get ready for next byte MOV P0, # “N” SJMP AGAIN
- 9. Example No. 4 Prepared By: Ms. K. D. Patil, Dept. of Information Technology, Sanjivani COE, Kopargaon 9 Write 8051 ALP to send FFH and 00H data serially using 8051 serial communication mode Solution: ORG 00H MOV TMOD,#20H ;timer 1,mode 2(auto reload) MOV TH1,#-3 ;9600 baud rate MOV SCON,#50H ;8-bit, 1 stop, REN enabled SETB TR1 ;start timer 1 AGAIN: MOV A, # 0FFh ACALL LOOP MOV A, # 00H ACALL LOOP SJMP AGAIN LOOP: MOV SBUF, A ; cleared for reception of data HERE: JNB YI,HERE ;wait for the character to come in CLR TI END
- 10. Importance of RI flag Prepared By: Ms. K. D. Patil, Dept. of Information Technology, Sanjivani COE, Kopargaon 10 In receiving bit via its RxD pin, 8051 goes through the following steps It receives the start bit Indicating that the next bit is the first bit of the character byte it is about to receive The 8-bit character is received one bit at time The stop bit is received, When receiving the stop bit 8051 makes RI = 1, indicating that an entire character byte has been received and must be picked up before it gets overwritten by an incoming character By checking the RI flag bit when it is raised, we know that a character has been received and is sitting in the SBUF register, We copy the SBUF contents to a safe place in some other register or memory before it is lost After the SBUF contents are copied into a safe place, the RI flag bit must be forced to 0 by CLR RI in order to allow the next received character byte to be placed in SBUF. Failure to do this causes loss of the received character
- 11. Importance of RI flag Prepared By: Ms. K. D. Patil, Dept. of Information Technology, Sanjivani COE, Kopargaon 11 By checking the RI flag bit, we know whether or not the 8051 received a character byte If we failed to copy SBUF into a safe place, we risk the loss of the received byte It must be noted that RI flag bit is raised by 8051 when it finish receive data It must be cleared by the programmer with instruction CLR RI If we copy SBUF into a safe place before the RI flag bit is raised, we risk copying garbage The RI bit can be checked by The instruction JNB RI, target Using an interrupt
- 12. Programming 8051 to Receive character byte Serially Prepared By: Ms. K. D. Patil, Dept. of Information Technology, Sanjivani COE, Kopargaon 12 1. TMOD register is loaded with the value 20H, indicating the use of timer 1 in mode 2 (8-bit auto-reload) to set baud rate 2. The TH1 is loaded with one of the values to set baud rate for serial data transfer 3. The SCON register is loaded with the value 50H, indicating serial mode 1, where an 8-bit data is framed with start and stop bits 4. TR1 is set to 1 to start timer 1 5. RI is cleared by CLR RI instruction 6. The RI flag bit is monitored with the use of instruction JNB RI, xx to see if the character has been received 7. When RI is raised, SBUF has the byte. Its contents are moved into safe place 8. To receive the next byte, go to step 5
- 13. Example No. 5 Prepared By: Ms. K. D. Patil, Dept. of Information Technology, Sanjivani COE, Kopargaon 13 Write 8051 ALP to receive data which has been sent in Serial form and send it out to Port 0 in parallel form Solution: MOV TMOD,#20H ;timer 1,mode 2(auto reload) MOV TH1,#-3 ;9600 baud rate MOV SCON,#50H ;8-bit, 1 stop, REN enabled SETB TR1 ;start timer 1 CLR RI ; cleared for reception of data HERE: JNB RI,HERE ;wait for the character to come in MOV A, SBUF ; move received data in A MOV P0, A
- 14. Reference Prepared By: Ms. K. D. Patil, Dept. of Information Technology, Sanjivani COE, Kopargaon 14 “The 8051 Microcontroller and Embedded Systems using Assembly and C” , Muhammad Ali Mazidi, Janice Gillispie Mazidi, Rolin D. McKinlay, Second Edition, Pearson publication
- 15. Prepared By: Ms. K. D. Patil, Dept. of Information Technology, Sanjivani COE, Kopargaon 15