Hello everyone. I have a project where 4 slaves (pic16F876) and 1 master
(pic16F877) will be using i2c to communicate. I'm pretty new to pics but
can do PicBasic easily enough. But the PicBasic i2c stuff doesn't work
for my project (why not?) and I need to use assembler to read and write
between the 16F877 and 16F876's. I've spent a few days on this already
without success and I'm getting confused about when to send Acks, Nacks,
Stops, etc. If some kind person could list the sequence of events for an
i2c read and an i2c write (on the master side - I believe the slave code
is fine) and what needs to be done in software and when it needs to be
done. I will be eternally grateful.



Although I need to do the read/write's  in assembler I'll be doing the
rest of the code in PicBasic (for speed: the code needs to be ready for
shipping at the end of this month). The most urgent difficulty is
getting the read to work. Here's where I'm at - at the moment  (it
doesn't work properly). Thank you very much for reading this and helping
out.



loop:

                        Pause 1000

                        currentAddress  = 17

                        call SetStart

                        call i2cSendAddress

                        call i2cReadByte

                        inData[0] = SSPBUF

                        call i2cAck

                        call i2cReadByte

                        call i2cNack

                        call i2cStop

        goto loop                                                   ' Do
it forever

end



asm

_SetStart

                        banksel PIR1

                        bcf PIR1, SSPIF

                        banksel SSPCON2

                        bsf     SSPCON2, SEN

                        btfsc     SSPCON2, SEN

                        goto $-1

                        bcf STATUS, RP0

                        return

endasm



asm

_i2cSendAddress

                        bcf STATUS, C

                        movf _currentAddress, w

                        banksel SSPBUF

                        movwf SSPBUF

                        banksel SSPSTAT

                        btfsc SSPSTAT, R_W

                        goto $-1

                        bcf STATUS, RP0

                        return

endasm



asm

_i2cReadByte

            banksel SSPCON2

            bsf SSPCON2, RCEN                            ;generate read
condition

            btfsc SSPCON2, RCEN

            goto $-1

            bcf STATUS, RP0

            return

endasm



asm

_i2cStop

            banksel PIR1

            bcf PIR1, SSPIF

            banksel SSPCON2

            bsf SSPCON2, PEN

            banksel PIR1

            btfss PIR1, SSPIF

            goto $-1



endasm



asm

_i2cAck

            banksel SSPCON2

            bcf SSPCON2, ACKDT

            bsf SSPCON2, ACKEN

            bcf STATUS, RP0

            return

endasm



Cheers,

Peter



P Duthie, software engineer, CDLtd




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