In SX Microcontrollers, SX/B Compiler and SX-Key Tool, robotworkshop wrote:

Here is an extra function to go along with the ISR based serial code.  There are times when I want to take a peek in the serial input buffer to see what the next character is but I don't want to pull it out just yet.  To do so I just made a copy of RX_BYTE and called it RX_CHKBYTE to check the next character in the buffer.  Before calling the RX_CHKBYTE function I usually just check rxBufCnt to see if it is greater than 0.  If not I don't bother calling it as I have other processing to do.  Adding the extra function was pretty simple as is just doesn't update the pointer and leaves the count alone.  Hopefully others will find this extra function useful.

' Use: aByte = RX_BYTE
' -- returns "aByte" from 8-byte circular buffer
' -- will wait if buffer is presently empty
' -- rxBufCnt holds byte count of receive buffer (0 to 7)

FUNC RX_BYTE
  ASM
    BANK  rxSerial
    TEST  rxBufCnt				' check buffer count
    JZ    @RX_BYTE				' wait if empty
    MOV   W, #rxBuf				' point to tail
    ADD   W, rxTail
    MOV   FSR, W
    MOV   __PARAM1, IND				' get byte at tail
    INC   rxTail				' update tail
    AND   rxTail, #%00000111			' keep 0 to 7    
    DEC   rxBufCnt				' update buffer count
    BANK  0
  ENDASM
  ENDFUNC

' Use: aByte = RX_CHKBYTE
' -- returns the tail value from 8-byte circular buffer but leaves
' -- it alone.  Will wait if buffer is presently empty
' -- rxBufCnt holds byte count of receive buffer (0 to 7)
' -- 2/21/2008 RLD

FUNC RX_CHKBYTE
  ASM
    BANK  rxSerial
    TEST  rxBufCnt				' check buffer count
    JZ    @RX_CHKBYTE				' wait if empty
    MOV   W, #rxBuf				' point to tail
    ADD   W, rxTail
    MOV   FSR, W
    MOV   __PARAM1, IND				' get byte at tail
    BANK  0
  ENDASM
  ENDFUNC

Best Regards,

Robert

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