I2C interface and TWI_FREQ

Forum 2005-2010 (read only) Software Interfacing
#1

Hello,
I am interfacing a device that only functions at 32khz, so I have changed my twi.h file to have:

/*** twi.h ***/
  #ifndef TWI_FREQ
  #define TWI_FREQ 32000L  //changed from 100000L
  #endif

My sketch functions perfectly, but I would like to change the twi header back to it’s original value (100000L). This is important so that I can distribute the code for use with unmodified headers. So I have tried writing:

/*** Spork's I2C sketch  ***/
  #define TWI_FREQ 32000L
  #include <Wire.h>

With the idea that the ifndef would let my value stay at 32000, but my communication fails when it is set this way, so I suspect that it’s still running at 100000. Is there any way to fix this without editing the header file?

(Running arduino version 0017)

Spork

#2

Is there any way to fix this without editing the header file?

In your sketch, after the call to wire.begin, you can override speed as follows:

  TWBR = ((F_CPU / 32000l) - 16) / 2;
#3

Great! Thank you.

#4