Serial communication between two microprocessor kits using 8251.

Aim:

Write a program in ALP to establish Communication between two processors using 8251.

Apparatus:

1. ADS-SDA-86-STA kit
2. 8251 Study card
3. Adapter, Keyboard, Cables, Etc . . .

Procedure:

Transmission

1. Connect 8086 kit PC using RS232 cable.
2. Connect Power supply to 8086 kit and 8251 interfacing kit(only blue( 5v) and black(0v) lines   Power cable to power supply)
3. Connect 8251 to 8086 using 50pin and 26pin bus.
4. Short 5 & 6 pins of JP9 in 8251 kit
5. Keep the DIP switch in 1 & 7 on (8086kit), open TALK, and go to options select target device as 8086 and Connect.
6. Change dip switch into 1 & 5on, once reset 8086 kit.
7. Go to file →Download hex file 
8. G-4000(on system keyboard), we can observe the output on 8251 kit.
9. Remove RS232 cable from 8086kit and connect it to 8251, transmitted data displayed on PC Monitor

Recieving

1. Connect 8086 kit PC using RS232 cable.
2. Connect Power supply to 8086 kit and 8251 interfacing kit (only blue( 5v) and black(0v) lines Power cable to power supply)
3. Connect 8251 to 8086 using 50pin and 26pin bus.
4. Short 1 & 2 pins of JP9 in 8251 kit
5. Keep the DIP switch in 1 & 7 on (8086kit), open TALK, and go to options select target device as 8086 and Connect.
6. Change dip switch into 1 & 5on, once reset 8086 kit.
7. Go to file →Download hex file 
8. Change the DIP switch into 1 & 7 on, once reset.
9. Remove RS232 cable from 8086 kit and connect it to 8251.
10. G-4000 (on 8086 kit keyboard) .enter
11. Give some input from system keyboard (Example press A, B, C, D enter),once reset 8086 kit That data will be received at 8086 kit at location FF00 (press E, enter address FF00 and press  Comma you will get the ASCII values of A, B, C,D).

Program:

.OUTPUT 2500AD
;PROGRAM TO TEST 8251 TRANSMISSION
CLOCK_FREQ EQU  1536000     ;8253 clock frequency
CTL_8251   EQU  3402H       ;8251 control port address
DATA_8251  EQU  3400H       ;8251 data port address 
TMR1_8253  EQU  3002H       ;8253 timer1 address
CTL_8253   EQU  3006H       ;8253 control port address
EXT_RAM_LC EQU  0000:FF00H  ;RAM location 
DBDT       EQU  F800:4F1FH  ;routine for display on data field
CNT_BAUD_9600_MODE16 EQU 000AH
CNT_BAUD_4000_MODE01 EQU 0140H
CNT_BAUD_2400_MODE16 EQU 0028H
CNT_BAUD_1200_MODE64 EQU 0014H
CNT_BAUD_0300_MODE64 EQU 0050H
MODE_WORD16 EQU CEH
MODE_WORD1  EQU CDH
MODE_WORD64 EQU CFH
;With the count calculated for various baud rates program is 
;written to test transmission part of 8251 using RS_232 standard
;Data characters can be sent to 8251 on an interrupt basis.So 
;to send characters on interrupt basis the TxRDY pin of the
;8251 is connected to an interrupt input through PIC 8259.
;***************************************
;PROGRAM TO TEST 8251 TRANSMITTING PART.
;***************************************
DSEG SEGMENT
        ORG     0 : 3000H
MSG DB 'TESTING 8251 IN ASYNCHRONOUS MODE',0DH,0AH,1BH
DSEG ENDS
CSEG SEGMENT
      ORG 0000 : 4000H 
      ASSUME CS : CSEG, DS : DSEG

START:
      MOV AX, 00H      ;initialisation of stack pointer
      MOV SS, AX        
      MOV SP, 2000H 
       MOV AX, 00H
      MOV DS, AX
       CLI
      CLD
       MOV BX, 0202H     ;initalisation of interrupt vector 
      PUSH CS
      POP AX           
      MOV [BX], AX      
      MOV BX, 0200H     
      LEA AX, CS : SRVC1
      MOV [BX], AX
      MOV DX, FFD8H    ;ICW1 
      MOV AL, 13H
      OUT DX, AL

      MOV DX, FFDAH    ;ICW2(interrupt vector address) 
      MOV AL, 80H           
      OUT DX, AL
      MOV AL, 0FH        
      OUT DX, AL                    ;ICW4 
       MOV AL, 0FEH
      OUT DX, AL                    ;OCW1(IR0 mask reset) 
      MOV BX, OFFSET MSG            ;BX points to message         
      MOV SI, EXT_RAM_LC            ;SI points to RAM locations
                                   ;where the characters written to 8251 are stored      
       MOV DX, CTL_8253             ;initialise timer1 in mode2
      MOV AL, 76H
      OUT DX, AL
     MOV DX, TMR1_8253        
      MOV AL, < CNT_BAUD_9600_MODE16  ;load the LSB count in
      OUT DX, AL                     ;timer1 count reg
      MOV AL, > CNT_BAUD_9600_MODE16  ;load the MSB count in
      OUT DX, AL                     ;timer1 count reg
      STI                                   ;enable interrupt
      MOV DX, CTL_8251               ;8251 control port address.Send   
      MOV AL, 00H                    ;0's to guarantee,device is in
      OUT DX, AL                     ;the command instruction format.
                                    ;Repeat the same four times 
       NOP
      NOP
      NOP
      NOP 
      OUT DX, AL
      NOP
      NOP
      NOP
      NOP
      OUT DX, AL
      MOV DX, CTL_8251       ;send internal reset command
      MOV AL, 40H            ;to return device to idle state
      OUT DX, AL
      NOP
      NOP
      NOP
      NOP
      MOV DX, CTL_8251       ;load the mode control word
      MOV AL, MODE_WORD16
      OUT DX, AL
      NOP
      NOP
     MOV DX, CTL_8251       ;load the command word
      MOV AL, 33H           ;when CTS* input of 8251 is
      OUT DX, AL            ;asserted low and the 8251 buffer
      NOP                  ;is ready for a character,the TxRDY 
      NOP                  ;pin will go high.Since TxRDY pin
                           ;is connected to the interrupt pin,as soon as TxRDY is set
      INTR
                           ;is enabled and the process jumps to service routine.     
BACK: NOP
      JMP BACK
      SRVC1: 
       MOV AX, 0000H
       MOV DS, AX          
       MOV AL, [BX]         ;message address stored in reg BX
       ADD BX, 01H          ;read the message byte by byte
       CMP AL, 1BH          ;check if the byte is a last byte 
       JNZ AHEAD 
       MOV BX, OFFSET MSG   ;if yes reinitialise the pointer 
       MOV SI, EXT_RAM_LC   ;to message and RAM location
       JMP SRVC1
AHEAD: MOV DX, DATA_8251    ;if not send the char to data port
       OUT DX, AL           ;of 8251 & also save in ram location
       MOV CL, AL
       MOV AX, 00H
       MOV DS, AX
       MOV AL, CL 
       MOV [SI], AL
       ADD SI, 01H
       STI
       IRET
CSEG ENDS
END

PROGRAM TO TEST 8251 RECEIVING  PART

.OUTPUT 2500AD
CLOCK_FREQ EQU  1536000    
CTL_8251   EQU  3402H      
DATA_8251  EQU  3400H       
TMR1_8253  EQU  3002H      
CTL_8253   EQU  3006H       
EXT_RAM_LC EQU  0:FF00H    
DBDT       EQU  F800:4F1FH  
CNT_BAUD_9600_MODE16 EQU 000AH
CNT_BAUD_4000_MODE01 EQU 0140H
CNT_BAUD_2400_MODE16 EQU 0028H
CNT_BAUD_1200_MODE64 EQU 0014H
CNT_BAUD_0300_MODE64 EQU 0050H
MODE_WORD16 EQU CEH
MODE_WORD1  EQU CDH
MODE_WORD64 EQU CFH

;************************************
;PROGRAM TO TEST 8251 RECEIVING PART.
;************************************

DSEG SEGMENT
     ORG 0000 : 3000H
DSEG ENDS
CSEG SEGMENT
      ORG 0000 : 4000H 
      ASSUME CS : CSEG, DS : DSEG
START:
      MOV AX, 00H      
      MOV SS, AX        
      MOV SP, 2000H 
      MOV DS, AX
      CLI
      CLD      
      MOV BX, 0202H      
      PUSH CS
      POP AX           
      MOV [BX], AX      
      MOV BX, 200H     
      LEA AX, CS : SRVC2
      MOV [BX], AX

      MOV DX, FFD8H    ;ICW1 
      MOV AL, 13H
      OUT DX, AL
      MOV DX, FFDAH   
      MOV AL, 80H           
      OUT DX, AL
      MOV AL, 0FH        
      OUT DX, AL       
      MOV AL, 0FEH
      OUT DX, AL         
      MOV BX, EXT_RAM_LC   
      MOV DX, CTL_8253      
      MOV AL, 76H
      OUT DX, AL
      MOV DX, TMR1_8253     
      MOV AL, <CNT_BAUD_9600_MODE16    
      OUT DX, AL
      MOV AL, >CNT_BAUD_9600_MODE16    
      OUT DX, AL
      STI              
     MOV DX, CTL_8251   
      MOV AL, 00H        
      OUT DX, AL         
      NOP
      NOP
      NOP
      NOP
      OUT DX, AL
      NOP
      NOP
      NOP
      NOP
      OUT DX, AL
      MOV DX, CTL_8251   
      MOV AL, 40H        
      OUT DX, AL
      NOP
      NOP
      NOP
      NOP
      MOV DX, CTL_8251   
      MOV AL, MODE_WORD16
      OUT DX, AL
      NOP
      NOP
      NOP
      NOP
      MOV DX, CTL_8251   
      MOV AL, 36H
      OUT DX, AL
BACK1: NOP
      JMP BACK1
SRVC2:
      MOV DX, DATA_8251
      IN AL, DX            
      IN AL, DX           
     NOP     
      NOP   
      NOP  
      NOP  
      CMP AL, 0DH 
      JNZ AHEAD2
      MOV AH, 00
      MOV SI, AX
      CALL FAR DBDT
      MOV BX, EXT_RAM_LC 
      JMP TERM
AHEAD2: MOV [BX], AL      
       INC BX            
TERM:  STI
       IRET
CSEG ENDS
     END

Result:

The Transmission Of 8251 Is Studied And The Output Is Verified

Updated
Oct 25, 2014
Views
9,554