I2C Slave with a PIC

[ralfmayr]

Some Remarks:

1. It is necessary to set the "DEFINE I2C_HOLD 1" in the master to get a
better behaviour of the timing. I checkrd it with the logic analyzer and it is
exactly like in the original "Phillips-Spec"

2. In the section
...
while STAT_BF = 1
i = SSPBUF ' Dummy Read inserted => clears BF Flag
wend
...
it is necessary to inlude the dummy read to get it work on
a 18F6722 and a 18LF14K22 (refer to MCHIP App Note 734, page 17)

3. Address range ist tested from 00h to FFh, all work well.

4. New address setting works (in the main loop) by only setting SSPADD
register with new value without reseting the complete handler.

Regards,
Ralf

[aratti]

ralfmayr wrote on 17th Feb. 2009

Hi Daniel,
no, i stopped working on it, it is not possible to get it work... :-(

I solved my problem using serin/serout.
But it would be great when we exchange our know-how, so we can solve this together!

-,Ralf

I quoted your last year post, just to congratulate with you for the remarkable knowledge you have gained in a year. This will teach new comer that persevering on a subject always pay.

Thank you for those additional I2C remarks that could be useful.

Al.

[ralfmayr]

Yep,
last year i made my first experiments with i2cslave,
but had no time to work on it for 8 months now as
i was very busy with other things.
Hope it will help others to come faster to their target.
-,Ralf

[ralfmayr]

Hello Al,
another question:
What are the three definitions:
1. DEFINE I2C_SLOW 1
2. DEFINE I2C_HOLD 1
3. DEFINE I2C_SCLOUT 1
do?
1. => Used with LO > 8MHz and 100kHz devices
2. => Time Delay during acknowledge?
3. => Open Collector / Bipolar Clock on SCL? Dont Understand this!

So: I use PCF8575C and MAX3611 (both 400kHz devices) but both only work
correct when DEFINE I2C_HOLD 1 and DEFINE I2C_SCLOUT 1 is done.

Can you help?

Regards,
Ralf

[Archangel]

Hello Al,
another question:
What are the three definitions:
1. DEFINE I2C_SLOW 1
2. DEFINE I2C_HOLD 1
3. DEFINE I2C_SCLOUT 1
do?
1. => Used with LO > 8MHz and 100kHz devices
2. => Time Delay during acknowledge?
3. => Open Collector / Bipolar Clock on SCL? Dont Understand this!

So: I use PCF8575C and MAX3611 (both 400kHz devices) but both only work
correct when DEFINE I2C_HOLD 1 and DEFINE I2C_SCLOUT 1 is done.

Can you help?

Regards,
Ralf

Hi Ralf,
I can answer part of #3:
Open collector means the PIC has 2 states LOW where it takes the pin to ground and an open state where the pin is high impedance, so to get a high state it must have a pull up resistor to supply the power. I do not know what bipolar clock means, have not read up on this yet.

[aratti]

1. => Used with LO > 8MHz and 100kHz devices

Yes.

2. => Time Delay during acknowledge?

Not Exactly, data transfer can be paused by the receiving device by holding the clock line low, so the receiving device can control the data flow. To enable this function you need the DEFINE I2C_HOLD 1 declared.

3. => Open Collector / Bipolar Clock on SCL? Dont Understand this!

Joe already answer to this point with a clear explanation. Let me add that bipolar is a device capable to pullup the lines by itself without the need of external pullup resistors

So: I use PCF8575C and MAX3611 (both 400kHz devices) but both only work
correct when DEFINE I2C_HOLD 1 and DEFINE I2C_SCLOUT 1 is done.

It is usefull to use DEFINE I2C_HOLD 1 as default since it will keep synchronized different devices connected on the I2C bus all with different internal clock.

I don't know much about PCF8575C and MAX3611 but very likely they are bipolar devices.

Al.

[ralfmayr]

Thank you both for the answers.
Now i understand.
So it seems always to be best to work with declaration 2 & 3 with
400 khz devices. This is what i found out yesterday.
Have nice eastern!
Regards,
Ralf