I2C issue w/ 18F6722

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- 15th July 2010, 23:12
circuitpro

I2C issue w/ 18F6722

I have not used a PIC18F6722 before, but needed two UART PORTS so decided to give it a try. I did not expect to have I2C issues, but when I try to do a read (of a PCF8574) using I2C port 1 it always returns DEC 16. When troubleshooting this, I pulled all the PCF8574's from their sockets, and also removed an EEPROM from the buss. Now the buss is empty except for two pullup 4.7K pullup resistors. It STILL returns DEC 16! I carefully examined the traces on the board, and they are clean and not tied to anything they shouldn't be. I also tried the same code on the second I2C port (which also has nothing on it but pullups) and it has the decency to return 0. To me that means that it's probably some conflict on port C, or other configuration error that I'm not aware of, or possibly a compiler error (2.60 Patch A).

Can anybody spot what I'm doing wrong?

Thanks,
Len

Code:

'PIC18F6722 ASM CLRF PORTC MOVLW 10000000b ;SET PIN DIRECTION MOVWF TRISC CLRF PORTD MOVLW 00000010b ;SET PIN DIRECTION MOVWF TRISC ENDASM DEFINE OSC 20 'XTAL FREQUENCY 'DEBUG PORT DEFINE DEBUG_REG PORTD 'DEBUG PINS ARE IN PORTD DEFINE DEBUG_BIT 0 'TRANSMIT DEBUG PIN IS PORTD.0 DEFINE DEBUG_BAUD 115200 '115200 BAUD DEFINE DEBUG_MODE 0 'NO INVERSION DEFINE DEBUGIN_BIT 1 'RECEIVE DEBUG PIN IS PORTD.1 X VAR BYTE TEST: I2CREAD PORTC.4,PORTC.3,%01000001,[X] 'DOESN'T WORK - ALWAYS RETURNS DEC 16 'I2CREAD PORTD.5,PORTD.6,%01000001,[X] 'WORKS DEBUG BIN8 X,10,13 PAUSE 500 GOTO TEST
- 16th July 2010, 00:03
mark_s

Try changing your TRIS registers.

It looks like you have them set to outputs both clk and data.

Not sure why you are using asm?
and you set trisc two time I think you wanted to set port D in the second statement

Try (without asm)
PORTC = 0 ; clear portc
TRISC =%0001000 ;set portc.4 to input all others outputs
PORTD = 0 ;clear port d
TRISD =%0010000 ;set portd.5 to input all others outputs

This matches your IC2READ statements , if you want to use other pins you need to change
the DATA and clock pin assignments

TEST:
I2CREAD PORTC.4,PORTC.3,%01000001,[X] 'DOESN'T WORK - ALWAYS RETURNS DEC 16
'I2CREAD PORTD.5,PORTD.6,%01000001,[X] 'WORKS
DEBUG BIN8 X,10,13
PAUSE 500
GOTO TEST

Regards
- 16th July 2010, 00:28
circuitpro

No difference. It is behaving the same way
- 16th July 2010, 14:55
mark_s

Quote:

Originally Posted by circuitpro

No difference. It is behaving the same way

Do you have a schematic? Which pins on the pic go to which pins on PCF chip?

Take a look in the manual under I2CREAD, you have to set your datapin and clockpin to match
the physical connection to the pic. Also TRIS must be set to match.
- 16th July 2010, 18:37
circuitpro

After reading thru the datasheet section on the MSSP modules, I'm sure it's my error in not setting something in the MSSP up properly. I will have to get down and really figure out what all these setup bits actually do when I get back in front of hardware later today. My first post was a little misleading by saying the second I2C port 'worked'. It returned '0', but there wasn't any hardware on the buss either. It also did not work with hardware on the buss. It just kept returning '0's. That points away from hardware (I've used this PCF8574's for years, and the hardware is connected right). It's the dummy driving the new PIC that's at fault. :-(
- 16th July 2010, 21:38
circuitpro

Code:

SSP1CON1.5=1 'ENABLE I2C #1 SSP1CON1.3=1 'SET I2C#1 FOR MASTER MODE SSP1CON1.2=0 'SET I2C#1 FOR MASTER MODE SSP1CON1.1=0 'SET I2C#1 FOR MASTER MODE SSP1CON1.0=0 'SET I2C#1 FOR MASTER MODE

fixed my problem. Apparently the PBP I2C command doesn't do any setting of this stuff for hardware I2C pins, so must be set.

Thanks for your help Mark.

Len