Using I2C on the Q2406B module


Has anybody used the I2C bus to comunicate with a External device?
for example to a external processor that handles time critical processes?


Yes, I used I2C for testing before… Didn’t get implemented in our current products. It is slow! I guess it is because it’s a software implementation…

I wouldn’t use it for time critical purposes, but it is fine to control an IO extender (for example to control more led’s as the module has ports…), or an external clock chip.

Best Regards,


Yes, Walter, you can use i2c on 2406 module.

But keep in mind:

  • Because of the software nature of i2c implementation, speed is very, very slow ~5-6 kbits. Bit rate may vary as well.
  • Protocol sometimes is not stateful (start-data-stop), for example when modem have +WIND changes.
  • You MUST pull-up BOTH wires externally.
  • You can use I2C only as master to address slaves

You can prototype with AT commands +WBM, +WBW and +WBR (see the manual for details)
With +WBM you can assing any GPIO for SCL and SDA.
+WBM may have 3 parameters, third one is I2C address:


means “write one byte on I2C address 0x35”
modem answer with data prompt

and you must enter 2 chars in hex notation, e.g. “4b” followed by ctrl-z

The easiest way to test communication with slaves is to send more bytes (2-5). If something goes wrong (slave not answer), communication stops after address stage and modem returns “ERROR”

As Jan says, I2C is useful for external extenders - LED, LCD display, relays, etc.



hi jan,vesskov,

i am new at open AT iam working on to interface a smartCard(memory)
with the wavcom module , using th T0 I2C protocol, please if you could provide some tips or templates, it would be of great help,…


My suggestion is to use external MCU for SmartCard related communications.


I’ve just been searching through the documentation, and couldn’t find this stated anywhere. :frowning:
Where is this requirement documented :question:

Does it apply to using the “soft” I2C on the GPIO4,5 pins of a Fastrack modem? (I guess it would)

What pullup value should be used?




Cross-post in the Fastrack forum: … =4535#4535