I2C speed

JPA · Guest

Hello,

When reading compiler updates, I see that since v3.215, the speed of I2C bus could be specified using FAST=xxxxx
"3.215 #USE I2C now allows the speed to be set in BPS using FAST=xxxxxxx"

Are there limits on the BPS value ?
Is this also available when using the hardware I2C ?

In my application, I have 2 I2C bus from the same chip:
-1 for accessing serial EEPROM, needs to be as fast as possible (max EEPROM clock frequency is 1MHz )
-1 for accessing expanded I/O, which are located 50cm away from the PIC, and needs to be slower (less data to transmit, minimize EMI/EMC problems)

Has anybody already try this feature and has some advices for me ?

Thanks for your answers.

Mark · Joined: 07 Sep 2003 Posts: 2838 Location: Atlanta, GA

JPA · Guest

With I2C hardware, I have to analyse the code in LST to see what they are doing. For the software implementation, I compiled the same code with several speed from 1000 BPS to 100 000 BPS and I have seen differences in the generated ASM code (low speed -> loop with different values, high speed -> a lot of nop). I suspect that these are relatives to delays changing and it seems they did it in software.

To be sure I need to look at the signals on the bus using my scope.

Anybody else tried this feature ?

Fabri · Joined: 22 Aug 2005 Posts: 275

Hi,

I'm also using I2C bus to comunicate with a control pannel. I have some problem with EMC with burst +- 2KV on power ac line. Especially when I connect the controll pannel with a cable of at least 50 cm. I use the same 6 wire cable to supply the pannel.

The main board do some reset but control pannel stop to work. I use watchdog to reset all if there's no any valid comunication but it work only in some case. I do some test on power supply of control pannel and it work fine also with burst.
Have you got to suggest me to solve the problem ?

Regards,
Fabri