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SOFTEARE UART TIMEOUT

Ricardo Pozza

Hello to all.
i have a software uart, writen in assembler, working fine, but i want to put a timeout if no byte is received or if dont have start bit.
It is external interrupt driven at int1, but really need the timeout because the byte sometimes dont arrive.

the assembler code below have a line that says "Wait for Start Bit", is where i want to put the timeout.

Can i put a loop that expires after x counts without start bit? how to do this in assembler?

Or i can start a timer when int1 interrupts, when the timer interrupt i set a flag in C, how to read this flag in assembler and stop waiting the start bit?

Thanks a lot for help and sorry my bad english

the code:

RSEG ?SU?GETC
 getc:
         Push ACC
         Push PSW
         JB rxd_pin,$            ;Wait for start bit
         MOV R0,#BITTIM/2        ;Wait 1/2 bit-time
         DJNZ R0,$                       ;To sample in middle
         JB rxd_pin,getc         ;Insure valid
         MOV R1,#8                       ;Read 8 bits
 getc1:
         MOV R0,#BITTIM          ;Wait full bit-time
         DJNZ R0,$                       ;For DATA bit
         MOV C,rxd_pin           ;Read bit
         RRC A                           ;Shift it into ACC
         DJNZ R1,getc1           ;read 8 bits
         mov r7,a
         POP PSW
         pop ACC
         RET                                     ;go home
         END

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