I2C Slave with a PIC

[rswain]

Guys,

This weekend I put together software nuggets from both DaveC3 and BigWumpus. In doing so, I could see the influence of most of you that have been working on this thread over the last few weeks. I went through and trimmed out the dead code, and moved a few things around to work for my uses. I'll post both the master and slave(s) in the next day or two so others can learn from our efforts! Thanks to everyone for taking on this tough problem.

Thanks,
rswain

[DanPBP]

Guys,

This weekend I put together software nuggets from both DaveC3 and BigWumpus. In doing so, I could see the influence of most of you that have been working on this thread over the last few weeks. I went through and trimmed out the dead code, and moved a few things around to work for my uses. I'll post both the master and slave(s) in the next day or two so others can learn from our efforts! Thanks to everyone for taking on this tough problem.

Hey rswain!

Any news about this?

Thanks!

Daniel.

[ralfmayr]

Hi all,
wanted to come back earlier with my experiences, but had too much work.
But :
I use Al's i2cslave in an 18F6722 I in an interrupthandler, in Al's code i made a little correction:

while STAT_BF = 1
i = SSP1BUF ' Dummy Read inserted => clears BF Flag
wend ' loop while buffer is full

This seems to be neccessary for this PIC's, the original code from Al results in
staying in this loop for ever.

I read back eight variables and write two variables with no problems.
The master and the slave have both the " DEFINE I2C_HOLD 1" at start up.

Regards,
Ralf

[ralfmayr]

Hi again,
did somebody test Al's code with a 18F14K22?
Regards,
Ralf

[ralfmayr]

There is an other problem with the i2cslave:

1. When the i2caddress is specifiead as constant (i2caddress CON $0F) it works perfect.

2. When bulding the address via a variable, it doesnt work:
...
i2caddress VAR byte
...
i2caddress = $0F

I need this because i build it from the status of four bits of Port A

Any idea?

Regards,
Ralf

[aratti]

I need this because i build it from the status of four bits of Port A

Any idea?

Ralf, you can try this:

Select Case PortA

Case 1
i2caddress CON $01
Case 2
i2caddress CON $02
case 3
i2caddress CON $03
.
.
.
.
Case x
i2caddress CON $x
End Select

It should work.

Edited:

No! it doesn't work sorry.

Al.

[Dave]

ralfmayr, Here is what I have been using for years. It uses the base address for the first of 3 PCF8574's. I then calculate the address depending on the one I need to gather or send data to.

UNIT0 CON %01000000 'U5's CONTROL BYTE (PCF8574) I/O EXPANDER

'**************** I2C I/O ROUTINE (PCF8574A) I/O EXPANDER ************
READ_WRITE VAR BIT 'READ DATA or WRITE DATA FLAG
EXPAND_UNIT VAR BYTE 'CONTROL BYTE FOR I2C
DEVICE VAR BYTE 'SELECTED I/O EXPANDER DEVICE
OUTPUTS VAR BYTE[3] 'RELAY OUTPUT BYTES
SWITCHES VAR BYTE[3] 'SWITCH INPUTS BYTES

'************************************************* *******************
R_WI2CS:'READ DIGITAL INPUTS FROM or WRITE DIGITAL OUTPUTS TO PCF8574'S
'************************************************* *******************
EXPAND_UNIT = UNIT0 'COPY BASE ADDRESS OF PCF8574'S
EXPAND_UNIT = (EXPAND_UNIT | (DEVICE << 1)) 'SELECT WHICH DEVICE
IF READ_WRITE = 0 THEN 'READ INPUT STATUS FROM PCF8574'S
I2CREAD SDA,SCL,EXPAND_UNIT,[SWITCHES(DEVICE)]
ELSE 'SET OUTPUT STATES TO PCF8574'S
I2CWRITE SDA,SCL,EXPAND_UNIT,[OUTPUTS(DEVICE)]
ENDIF
RETURN


Then to use it first set the device index.
Next set the read_write flag.
Then finally call the routine.....

Dave Purola,
N8NTA