Here is an SPI routine that is not working - see attached analyzer log.
For some reason the Serial Out (SO) line (when high) is falling at clock rise but I can't figure out why. Any ideas? Perhaps it's staring me in the face because I've been debugging it for too long. Probably just need somebody else to have a look...
Any thoughts?
..or is it an electrical problem? Do I need any resistors or other components between the PIC12F675 and the ENC28J60? Currently it is a direct connection on a breadboard.
Thanks,
David
For some reason the Serial Out (SO) line (when high) is falling at clock rise but I can't figure out why. Any ideas? Perhaps it's staring me in the face because I've been debugging it for too long. Probably just need somebody else to have a look...
Code:
;-----------------------------------------------------------------------------------------------------------------------------
; SPI subroutine
; ==============
;
; Call with:
;
; spi_count set to the number of bytes to write/read
; spi_in set to the first register address of the inbound buffer
; spi_out set to the first register address of the outbound buffer
;-----------------------------------------------------------------------------------------------------------------------------
spi
movlw spi_in1
movwf spi_in ; Set the start of the inbound buffer
movlw spi_out1
movwf spi_out ; Set the start of the outbound buffer
movlw 8 ; Set bit counter
movwf spi_bit ; to 8 bits
bcf GPIO,2 ; Set CS line low
spi_looplong
nop
nop
nop
nop
nop
nop
nop
spi_loop
movf spi_out,W ; Point to next spi_out byte
movwf FSR ; with File Select Register
rlf INDF,F ; Roll next data bit into Carry flag
btfss STATUS,C ; Is it high? If yes, skip...
goto BitLow
bcf GPIO,1 ; **** Set clock line low ****
bsf GPIO,4 ; Set SO line high
goto spi_donebit ; We have done the bit, continue on...
BitLow
bcf GPIO,1 ; **** Set clock line low ****
bcf GPIO,4 ; Set SO line low
nop ; Wait an extra cycle if BitLow to match high alternative
spi_donebit
nop
nop
nop
nop
nop
nop
nop
nop
nop
nop
nop
nop
nop
nop
nop
nop
nop
nop
nop
nop
nop
nop
nop
nop
bcf STATUS,C ; Clear the Carry flag
bsf GPIO,1 ; **** Set clock line high ****
btfsc GPIO,5 ; Read bit from SI line, skip if clear (0)
bsf STATUS,C ; Set the Carry flag if bit not clear (1)
movf spi_in,W ; Point to next spi_in byte
movwf FSR ; with File Select Register
rlf INDF,F ; Roll the incoming bit into the buffer
nop
nop
nop
nop
nop
nop
nop
nop
nop
nop
nop ; Wait an extra cycle to match other side of clock
decfsz spi_bit,F ; Decrement bit counter, skip if zero
goto spi_looplong ; Go do next bit...
decfsz spi_count,F ; Decrement our byte counter, skip if zero
goto spi_nextbyte ; Go do next byte, otherwise...
nop ; Wait 210ns (each instruction is 1us or 1000ns)
nop
nop
nop
nop
nop
nop
nop
nop
nop
nop
bsf GPIO,2 ; Set CS high
return ; Return to program
spi_nextbyte
movlw 8 ; Reset bit counter
movwf spi_bit ; for next 8 bits
incf spi_out,F ; Point to next byte in outbound buffer
incf spi_in,F ; Point to next byte in inbound buffer
goto spi_loop ; Go do next byte...Any thoughts?
..or is it an electrical problem? Do I need any resistors or other components between the PIC12F675 and the ENC28J60? Currently it is a direct connection on a breadboard.
Thanks,
David