Update: 3 May 2003

As part of a class project I've taken it upon myself to convert these i2c
routines into a general purpose I2C template for devices containing the
I2C module. I expect to produce a general purpose template within the next few days using John Sands original code.

--Matt Krutar

PIC Microcontoller Input / Output Methods for I²C on 16F87x

by John Sand [jsand at PIXIE.CO.ZA]

I cribbed, borrowed and stole whatever I could, then went back to the 16f87x manual and wound up with a set of master transmit <> receive routines that are *working* - perfectly well as far as I can tell.

This app. has two Philips PCF8574 I2C general purpose byte-wide IO port chips. One (IO1) is dedicated to inputs only, for switch states, etc., while IO2 is output only, to drive a collection of panel LEDs. I have used private macros like :-

 bank0 ;use ram bank0
 bank1 ;use ram bank1
 movlf ;load literal to freg
 movff ;load freg1 to freg2

etc., these should need no introduction, but if they do, let me know.. Setup the ports by :-

 setup_i2c

Invoke a IO1 port read by:-

 read_switches ;byte-wide result in freg`latest_switch_state'

Invoke a IO2 port write by:-

 ;put desired byte into freg
'led_state'
 write_leds

;****************** I2C macros begin
start_i2c MACRO ;[S]
 bank0 ;bank0 (bank0? names) be sure
 bcf PIR1,SSPIF
 bank1 ;bank1
 bsf SSPCON2,SEN ;send i2c START [S] bit
 bank0 ;bank0
 btfsS PIR1,SSPIF ;start bit cycle complete?
 goto $-1
 endm
enable_receive_i2c MACRO
 bank1 ;bank1
 bsf SSPCON2,RCEN ;enable receiving at master 16f877
 bank0 ;bank0
 bcf PIR1,SSPIF
 btfsS PIR1,SSPIF ;sspbuf buffer full byte?
 goto $-1
 endm
stop_i2c MACRO ;[P]
 bank0 ;bank0
 bcf PIR1,SSPIF
 bank1 ;bank1
 bsf SSPCON2,PEN ;send i2c STOP [P] bit
 bank0 ;bank0
 btfsS PIR1,SSPIF ;stop bit cycle completed?
 goto $-1
 endm
wait_for_ack_i2c MACRO
 bank0 ;bank0
 bcf PIR1,SSPIF
 btfsS PIR1,SSPIF ;ACK received?
 goto $-1
 endm
setup_i2c MACRO ;setup mssp for i2c
 movlf 00101000b,SSPCON ;=0x028
 bank1
 movlf 10000000b,SSPSTAT
 movlf 01100000b,SSPCON2
 movlf 00001010b,SSPADD
 bank0
 endm
read_switches MACRO ;io1 is inputs only
 start_i2c
 movlf 01000011b,SSPBUF ;send out io1 pcf8574 addr
 wait_for_ack_i2c
 enable_receive_i2c
 movff SSPBUF,latest_switch_state
 stop_i2c
 endm
write_leds MACRO ;io2 is output only
 start_i2c
 movlf 01000100b,SSPBUF ;sned out io2
address, writing
 wait_for_ack_i2c
 movff led_state,SSPBUF
 wait_for_ack_i2c
 stop_i2c
 endm
;***************** I2C macros end

.