I2c

prograu I2C
' pic 16F87
'SENDS START CONDITION,3 BYTES, THEN STOP CONDITION ON I2C BuS TO SLAVE.
' PORTB.0 IS SCL LINE. PORTA.7 IS SDA LINE. DELAYS ARE FOR BETTER SCOPE DISPLAY
'10k pullup resistors required on sda and scl pins
dim tmp,bit,bite as byte
' not implemented yet
'const tda_adr as byte=$88
'const sub_adr as byte[9]=($00,$01,$02,$02,$02,$02,$02,$02,$02)
'const data    as byte[9]=($00,$00,$01,$03,$05,$07,$09,$0b,$0D)
uain:
osccon=%01100010            'cpu clock(Fosc)=4 uhz
while iofs=1                ' wait for clock to stabilize
wend
cmcon=7                     ' turn off adc
portb.0=0                   ' portb.0 scl
porta.7=0                   ' porta.7 sda

' trisb=0 => portb is output. since portb=0 portb.7=logic 0
' trisb=128=> portb.7 is input. with nothing to pull the voltage low
' Rpu will will pull the voltage high and portb.7=high
test_loop:

I2C_Start:
trisb=1
trisa=128
delay_us(50)
trisa=0
delay_us(50)
trisb=0
for bite=1 to 3  ' send 3 bytes on I2C bus
    if bite=1 then tmp=%10001000'tda chip address
    end if
    if bite=2 then tmp=%00000000 'tda sub_adr=#00000000=input selector
    end if
    if bite=3 then tmp=%00000010  ' tda_data=#00000000=select input#4
    end if
for bit= 0 to 7
trisb=0
delay_us(50)
        if tmp and 128=128 then
        trisa=128              'set tda high if current tda_data bit is high
        else trisa=0           ' else set tda low
        end if
        tmp=tmp << 1           ' shift current tda_data bit to uSB of tup
delay_us(50)
trisb=1
delay_us(100)
next bit

trisb=0
delay_us(50)
'ack
trisa=128
delay_us(50)
trisb=1
delay_us(50)
trisb=1
delay_us(50)
trisb=0
next bite

delay_ms(900)

for bit= 0 to 7      ' send another data byte to select input#4
trisb=0
delay_us(50)
        if tmp and 128=128 then
        trisa=128
        else trisa=0
        end if
        tmp=tmp << 1
delay_us(50)
trisb=1
delay_us(100)
next bit

trisb=0
delay_us(50)
'ack
trisa=128
delay_us(50)
trisb=1
delay_us(50)
trisb=1
delay_us(50)
trisb=0
delay_ms(999)

i2c_stop:
delay_us(40)
trisb=1
trisa=0
delay_us(20)
trisa=1
delay_us(20)

goto test_loop  '  scope shows on- off of audio input- it lives !
end.