I2C port questions

[landon]

I was reviewing some of the I2C XMOS code in the example: module_i2c.1v1 and noticed this code:

Code: Select all

  // turn the data to input
   i2c.sda :> Temp;
   gt :> time;
   time += (I2C_BIT_TIME / 2);
   gt when timerafter(time) :> void;
   i2c.scl <: 1;

// sample first ACK.
   i2c.sda :> ack[0];
   gt :> time;
   time += (I2C_BIT_TIME / 2);
   gt when timerafter(time) :> void;
   i2c.scl <: 0;

Is it necessary to do that i2c.sda :> Temp; call to turn the port into an input? I haven't ready anywhere in the XMOS XC port docs that to switch directions you needed to do one of these dummy inputs.

Is this how an XMOS I2C master "releases" the I2C bus so the slave can drive it?

Landon

[rp181]

In my experience, yes you do. It tripped me up for a long time, because one of the parts of hardware I use waits until the port becomes an input. So when I read the value, I got nothing, and then the hardware put out the data (when i wasn't listening). I had to put 2 consecutive read statements.

[landon]

Thanks for the confirmation. I was having trouble with this as well when I wrote some bit banging I2C today...it wasn't making sense so I started digging around and found that code above.

Once I put i a dummy read, it appeared to release the line.

Thanks again for the info,

Landon

[daleonpz]

Im new with XS1-L1, and i would like to know how to communicate the module with an ADC using I2C. :oops:

[landon]

I haven't done an I2C ADC interface with XMOS, only SPI. I'd suggest a couple things - look through all the example code available on xmos and xcore - there are definitely some I2C examples for other devices that could help you get started. Secondly, you might want to start a separate thread on the topic.