Hello Achim & PIC.ers,

I've had to bash my own way thru this recently meself...
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




>Date:    Fri, 26 May 2000 09:05:15 +0200
>From:    Achim Vollhardt <avollhar@PHYSIK.UNIZH.CH>
>Subject: [PIC]: I2C master mode routines for 16F877
>
> I am looking for some experienced guys working with the 16F877 as
>master
> with I2C protocol.. I have tried to figure out some working routine
>from
> the datasheet, but in contrast to the USART programming there is no
> 'to-do' list for I2C Master mode.. can anyone help me out as my own
> routines don't work ?
>
> Thanks in advance!
> Achim Vollhardt
>
> avollhar@physik.unizh.ch
>


Hope this all makes sense,

best regards,   John


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