I2C with 18F2685

[MikeBZH]

Hello,

I am trying, unsuccessuly up to now, to make some I2C communications between a 18F2685, a DAC (MAX517) and two I/O expanders (23008), everybody is on the same I2C bus, the DAC receiving data from the PIC and the I/O expanders being read by the PIC.

I would like to use the PBP commands I2CREAD and I2CWRITE but they look to be written for older PICS.

Do they also work with 18F PICS ? If yes, do I need to make some kind of preliminary initialisation, for example set up the I2C pins via TRISC or configure the MSSP registers ? Do I need to setup the bus speed or anything else (address width for example ?)

I have an other question about the addresses. They are supposed to be 7 bits width, but they look as being left justified. So, do they need to be passed to the PBP instructions as left justified or right justified variables. For example how should I pass the address $2c : $2c or $58 ?

Any help greatly appreciated

Best regards

MikeBZH

[Dave]

MikeBZH, Its in the manual.... And there is no difference whether its for an 16 series or 18 series..

Dave Purola,
N8NTA

[aratti]

I use both I2CRead and I2CWrite with pic18F4680 without any problem.

In my code I use always the following two declarations:

DEFINE I2C_SLOW 1
DEFINE I2C_HOLD 1

Al.

[MikeBZH]

Dave, Aratti

So it is so simple ?
I'll try this tomorrow.

Many thanks for your help

MikeBZH (also F8DFN, 73's Dave)

[MikeBZH]

Good evening !

No way with this problem !
I have spent the whole day on it with no result...

The circuit is yet very simplified : only the 18F2685 + the MAX517 + 2 pull-up resistors. The PIC is running at 32 MHz.

The program is also very simple and starts with :

DEFINE I2C_SLOW 1
DEFINE I2C_HOLD 1
....

AppGain:

Gain = $55
RESET517 = $10
CTRL517 = $00

Re2 : I2CWRITE PORTC.4,PORTC.3,CTRL517,ADR517,[Gain],Re1
PAUSE 10
GOTO Re3

Re1: ADR517 = ADR517 + 1
if (ADR517 <> $FF) then
goto Re2
else
endif

Re3: RETURN

All the variables are bytes.
AppGain is called by a test section of my program.

The hereabove version was adapted to scan the addresses in search of a response from the MAX517. According to the manual, the program jumps to Re1 if no ACK was received from the slave. And there is never any ACK received, the program always ends with $FF in ADR517. The slave address should be $2c but I got no answer from there.

I have checked the SDA and SCL lines with my scope. The signals look fine but no ACK is visible. I have even changed the MAX517 for a new one : same behaviour.

Any idea ?

MikeBZH

[Dave]

MikeBZH, What values are you using for the pullup reststors on the SDA/SCL lines... I have found in the past that 4.7 k resistors are too large and slow the current flow for passive pullup when I use more than 4 devices on a bus... I would use 2.2 k resistors and try that.. It should cleanup the data signal a bit.. I'm not sure if the statement DEFINE I2C_HOLD 1 is required or not.. I have never used it in the past and I have used 100 khz. parts and 400 khz. parts with no issues.. Just make sure you use the statement DEFINE I2C_SLOW 1 if the part is only good for 100 khz. and you are running the processor at more than 4 mhz..

Dave Purola,
N8NTA