Edson,

I have implemented the routine you mention for the 17c44; I think it
could be adapted to the 877 with almost no change. I use it for
receiving chars from the serial port of the computer.

The buffer is 16 bytes long, and starts from 0x20.
recNum is the number of bytes actually stored in the buffer.
recPtr is the pointer to the last received byte.
This is the chunk of code for initializating the FIFO:

......
        clrf recNum     ;set the FIFO to empty
        movlw 0x20              ;set the next byte to the FIFO base
        movwf recPtr
......


Next is the receiving (FIFO in) routine. I adapted it from a multiple
bytes receiving routine; in this case it receives just one byte at a
time. Maybe it could be semplified somehow.
rec1Byte is a routine which receives one byte from the serial port; it
returns with the received byte in tmpReg2, the number of received bytes
in tmpReg1 (this is 1 in this case), and an error code in errCode (0 for
no error; this is also used to complete reception and exit the routine).

recLoop
        call rec1Byte
        movlb 0
        tstfsz errCode
        goto recCompl                   ;an error occurred
        movwf tmpReg2
        movfp recNum,WREG
        incf recNum
        addwf recPtr,0
        bcf WREG,4
        movwf FSR0
        movfp tmpReg2,INDF0
        decfsz tmpReg1
        goto recLoop


Next is the fetching (FIFO out) routine. If the buffer is empty, it
returns with an error code in errCode (0 for no error), else it returns
with the fetched byte in WREG

fetchNextRcCh
        movlb 0
        clrf errCode
        tstfsz recNum
        goto valChar
        movlw eEmptyRecBuf
        movwf errCode
        retlw 0xff
valChar
        movfp recPtr,FSR0
        decf recNum
        incf recPtr
        bcf recPtr,4
        movfp INDF0,WREG
        return


Hope this helps.

Regards
Leonardo Perretti
leo.perretti@projectpp.it


Edson Brusque wrote:

>    anyone here have implemented a FIFO (First In, First Out) buffer for the
>hardware USART of a PIC? I'm using a PIC16F877 and it does have to receive
>USART and put it on a buffer for later processing.

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