I2C with 18F2685

[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

[MikeBZH]

Hi,

I fixed it, but the result is very strange.
Resistors values or Defines have no influence but it seems that there is bug in the PBP documentation (or in the compiler, as you prefer).

I found that the instruction :
I2CWRITE DataPin, ClockPin, Control, [Address,] ...

should be written
I2CWRITE DataPin, ClockPin, [Address,] Control...

In other words everything works if one pass first the Address and then the Control instead of what is written in the documentation. This is very clear with a dual trace scope on SDA and SCL.

My compiler version is 2.50L

MikeBZH / F8DFN

[MikeBZH]

Moreover,

The physical address has to be shifted left once (multiplied by 2) to cope with the I2C format. In my case the physical address is $2C : I have to pass $58 to I2CWRITE.

MikeBZH / F8DFN

[Melanie]

Strange... I use PBP v2.50 I2C to talk to EEPROM 24LC64, DS1307 and MCP23008 and other devices on the same board and it all behaves as expected per the Manual...

[MikeBZH]

Hi Melanie,

Please note that I use PBPL. Maybe the behaviour of this version is different from the others. I have no more time to make some comparison tests but I will do them when I come back from vacation by the end of August.

MikeBZH / F8DFN

[MikeBZH]

Hi,

Coming back after some time spent with other business...
I have no more MAX517 in my circuit but the MCP23008 are still there and I need to use I2CWRITE and I2CREAD with them.
The issue is still there. I confirm that with my PBPL v2.50, I need to invert the address and the control fields and to multiply the address by 2 to make I2CWRITE work. And from the experiments done this morning I know that I need to do the same thing for I2CREAD !

Best regards

MikeBZH / F8DFN

[Dave]

MikeBZH, I hope you had a nice vacation in August... I have been currently using a pair of 24LC1025's to log data from my Solar Tracker which uses an 18F2620 running @ 40 Mhz. I have had no problem with them even in the below zero temperatures we have up here in Michigan...
I do not compile with PBPL as I have used the internal flash to about 3/4"s of its capacity. It's nice to see you back...

Dave Purola
N8NTA