Need help with Propeller as an I2C slave using spin

Mike G

I’m trying to get the Propeller to act as a I2C slave device using spin. I’ve been racking my brain on this for a while now. I tried several approaches starting with looping and conditions that monitor the INA register. Then I moved on to using WAITPEQ (State, Mask, Port ) to detect the start of data transfer; SDA going low while SCL is high.

  WAITPEQ(%11, %11, 0) ' SCL = high SDA = high (Bus not busy)
  WAITPEQ(%10, %11, 0) ' SCL = high SDA = low (Start) 

WAITPEQ is not an ideal solution because I need a timeout. I’m just trying to get anything working.

My setup is a BS2p executing the following loop.

Main:
  I2COUT 0, $A0, %0001, [noparse][[/noparse]%0010, %0011]
  PAUSE 100
  GOTO Main

I’m using 1k inline resistors going to the Propeller and 4.7K pull-ups to Vcc.

I attached the scope output. It’s kinda’ strange to me that the scope output shows 0xA0 seven times then %0001, [noparse][[/noparse]%0010, %0011]. I’m expecting one 0xA0. Thought it might have something to do with the ACK bit. I can’t seem to hit ACK on the 9th clock pulse.

How can I sense a start condition “high-to-low transition of the SDA line while the clock (SCL) is high” using SPIN? I think if I can get that working I should be able to figure out the rest. Should I be using PASM?

John Abshier

I don't know if these work.· Use at you own risk and please report back.

John Abshier

Mike G

Thanks John, I'll give this a shot when after work.