Andrew Farrar wrote:
>
> Hello,
>
> I have a time critical application where each bit to be sent out
> serially is to have duration of 69uS (.02/288 to be precise, but 69uS
> will do).  I have a routine for serial transmission, modified from
> the embedded control applications book. However, I wish the time for
> each bit to be the same duration.  Is there a good way of doing this?
> Also when fetching another data byte to be sent and then converting
> serially, although I expect some padding can be done when sending
> bits to allow for the overhead involved in fetching the next byte.
>
> Can a simple modification be done to the code that I have:
>
> ; FILE SAVED  AS MAGIC2.ASM
> ; MAGIC1.ASM HAS BEEN TRASHED
>
> ; FOR PIC 16C84
>
>         CBLOCK 0X00
>         INDF,RTCC,PC,STATUS,FSR,PORTA,PORTB
>         ENDC
>
> BIT_COUNT       EQU 08H
> BYTE_COUNT      EQU 0CH
>
> DATA0           EQU 09H
TEMP    EQU     0DH     ;tempor.data reg
>
> F       EQU 1
> W       EQU 0
>
> Z       EQU 2   ;ZERO FLAG
> C       EQU 0   ;CARRY FLAG
>
> #DEFINE TX_0    PORTB,7 ; THIS IS SINE + 0 LINE
>
> ;**************IT STARTS HERE*****************
>
>          ORG      0
>          GOTO     START
>
>          ORG      30
>
> START   CLRW            ; PUT 0 IN WORK REG
>         TRIS    PORTB   ; SET UP PORTB ALL OUTPUTS
>         TRIS    PORTA   ;PORT A AS ALL OUTPUTS AS WELL
>
>         MOVLW   0
>         MOVWF   BYTE_COUNT
>
> NEXT_BYTE
>         MOVLW   .8
>         MOVWF   BIT_COUNT       ;START BIT COUNT AT 8 (TO GO)
>         MOVLW   .3     ; MODIFY LATER, SORT ONE BIT OUT AT A TIME !
>       CALL    MAGIC   ; AFTER WHICH W CONTAINS FIRST BYTE OF DATA
>    MOVWF   DATA0
>
> ;TRANSMIT SECTION
>
> SEND_ANOTHER_BIT
        clrf    TEMP
>         RLF     DATA0,F    ; CARRY FLAG TO CONTAIN SERIAL DATA
>         BTFSC   STATUS,C
        bsf     TEMP,7          ;as TX_0
        movf    TEMP,W
        movwf   PORTB
;         BSF     TX_0    ;TRANSMIT A ONE
;         BTFSS   STATUS,C
;         BCF     TX_0    ;TRANSMIT A ZERO
>         DECFSZ  BIT_COUNT,F
>         GOTO    SEND_ANOTHER_BIT
>         GOTO    NEXT_BYTE
>
> MAGIC   ADDWF   PC,F    ; ADD OFFSET TO PC AND GET MAGIC DATA
>         RETLW   000h
>         RETLW   090h
>         RETLW   034h
>         RETLW   0C3h
>         RETLW   0E6h
>         RETLW   0BBh
>         RETLW   0DDh
>         RETLW   0F7h
>         RETLW   0F7h
>
>         END
>
> The program is by no means complete but any help or suggestions, on
> the problem of a '1' having duration of 10uS and a '0' of 6uS would
> be appreciated, please correct me if these figures are wrong!
>
> NB C3 was chosen for now as all being well this should give a square
> wave if repeated 1100 0011 1100 0011 1100 0011.
>
> Many thanks for getting this far, hope very much that you can help.
>
> Cheers
>
> Andy Farrar
> asf@ee.port.ac.uk
B.R. Vladimir