A new function for ISR based serial receive code.

RobotWorkshop

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