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Bitbanging code help for 8051!!

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nerdspot

nerdspot

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mov r0,#bittim

I got a bit banging code online from **broken link removed**, sorta modified it and used it for my AT89C51. I'm using a 3.5795Mhz clock and a 300 baud transfer rate. Can some one help me out with a valid bit banging code? It sends the number 9 and receives it on another 8051 and displays the result on port0 on 8 LED's. now the problem is, when i connect it, all the LEDs light up or sometimes, they light up randomly. Please help..
 

Your code :
Code: 
;Rx at another AT89C51
SEND EQU P1.0 ;Transmit on this pin
RECV EQU P1.1 ;Receive on this pin
; The serial baud rate is determined by the processor crystal, and
; this constant which is calculated as: (((crystal/baud)/12) - 5) / 2
BITTIM EQU 494 ;(((3579545/300)/12) - 5) / 2
;
getc:
loop: 
  JB    RECV,loop     ; Wait for start bit
  MOV   R0,#BITTIM/2  ;Wait 1/2 bit-time
loop1: 
  DJNZ  R0,loop1      ; To sample in middle
  JB    RECV,getc     ;Insure valid
  MOV   R1,#8         ;Read 8 bits
getc1: 
  MOV   R0,#BITTIM    ;Wait full bit-time
loop2: 
  DJNZ  R0,loop2      ; For DATA bit
  MOV   C,RECV        ;Read bit
  RRC   A             ;Shift it into ACC
  DJNZ  R1,getc1      ;read 8 bits
  MOV   P0,A
  
  END

After excute MOV P0,A 8051 is loss control, we don't know what it'll doing, so you see :
all the LEDs light up or sometimes, they light up randomly.
Click to expand...

Add SJMP $ after MOV P0,A
 

    nerdspot

    nerdspot

    Points: 2
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then how do i display any data? Do i loop the txd and rxd instructions? is my modification of the bitbanging code correct?

Added after 6 minutes:

so, with $, it'll loop back to the first address.. right? but i have to do that to the transmitter too or there wont be any data received, correct?
 

SJMP $ is equivalent to :
Code: 
Here:
     SJMP Here
it is the way to "stop" 8051

If you want repeat the whole process replace SJMP $ with SJMP getc, and add SJMP putc at the other program
 

    nerdspot

    nerdspot

    Points: 2
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Cool.. Thx man.. will try it out tomorrow and post.. Do i have to put SJMP $ for the transmitting too?
 

Do i have to put SJMP $ for the transmitting too?
Click to expand...
It depend on you, whether you want stop the processor (use SJMP $) or you want repeat the process (use SJMP getc and SJMP putc).
 

    nerdspot

    nerdspot

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When i run the code(with the modified code) in both the transmitting and recieving uc, no LEDs glow.
 

Transmitter:
Code: 
;Tx from one AT89C51
SEND EQU P1.0 ;Transmit on this pin
RECV EQU P1.1 ;Receive on this pin
; The serial baud rate is determined by the processor crystal, and
; this constant which is calculated as: (((crystal/baud)/12) - 5) / 2
BITTIM EQU 494 ;(((3579545/300)/12) - 5) / 2
;
; Transmit character in A via TXD line

putc:
      MOV   A,9
      CLR   SEND           ;Drop line for start bit
      ACALL bittime        ;start bit
      MOV   R1,#8          ;Send 8 bits
putc1:
      RRC   A              ;Move next bit into carry
      MOV   SEND,C         ;Write next bit
      ACALL bittime        ; data bits
      DJNZ  R1,putc1       ;write 8 bits
      SETB  SEND           ;Set line high
      ACALL bittime        ;stop bit
      SJMP  putc

bittime:
      MOV   R0,#BITTIM     ;Wait full bit-time
      DJNZ  R0,$
      RET

      END

Receiver:
Code: 
;Rx at another AT89C51
SEND EQU P1.0 ;Transmit on this pin
RECV EQU P1.1 ;Receive on this pin
; The serial baud rate is determined by the processor crystal, and
; this constant which is calculated as: (((crystal/baud)/12) - 5) / 2
BITTIM EQU 494 ;(((3579545/300)/12) - 5) / 2
;
getc:
       JB    RECV,$             ;Wait for start bit
       MOV   R0,#BITTIM/2       ;Wait 1/2 bit-time
       DJNZ  R0,$               ;To sample in middle
       JB    RECV,getc          ;invalid startbit
;
       MOV   R1,#8              ;Read 8 bits
getc1:
       MOV   R0,#BITTIM         ;Wait full bit-time
       DJNZ  R0,$               ;For DATA bit
       MOV   C,RECV             ;Read bit
       RRC   A                  ;Shift it into ACC
       DJNZ  R1,getc1           ;read 8 bits
;
       MOV   P0,A
       SJMP  getc

       END

I don't see any error on your code. Try again!

Re-check the circuit connection, don't forget P1.0 of Transmitter connect to P1.1
of Receiver
Turn on Receiver supply first, after that turn on transmitter
 

    nerdspot

    nerdspot

    Points: 2
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Hi,

budhy said:
Turn on Receiver supply first, after that turn on transmitter
Click to expand...

absolutly correct, some months back i wasted many hours in a project due to this problem.



thanks
sawaak
 

    nerdspot

    nerdspot

    Points: 2
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Is
Code: 
MOV   A,9
the correct way of moving the number 9 to the acc? Does it have to be
Code: 
MOV   A,#9
 

Yes, it have to be :
Code: 
        MOV   A,#9

but it doesn't make receiver can't receive any thing (P0 display nothing, no LEDs glow), except content of memory #9 = 0 or memory #9 = 0xFF (depend on your LED circuit)
 

    nerdspot

    nerdspot

    Points: 2
    Helpful Answer Positive Rating
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