SPI with 2 wires only

Forum 2005-2010 (read only) Hardware Interfacing
1

Hi is it possible to use the SPI protocol with 2 wires only?
I have the CLK and SDA connection available, but not the SPO pin.

Hi, I'm trying to connect an MMA7455L freescale accelerometer that I bought mounted on a PCB.
You can see it at:

Thanks for your help!
Cristian

2

Most SPI devices need the chip select signal as part of the latching process for the messages. However not all do, you would have to experiment with your device to see if it worked without the chip select phase, but I suspect not.

3

Hint: SDA and SCL are the common signal names for I2C, not SPI. I2C is a two wire interface.

-j

4

Yep, missed the fact that the OP had got the title completely wrong.
My answer still stands for an PI interface.
Have you got the ground of this device connected to the arduino ground?
Are you using the correct address, this should be the 7 bit format not the 8 bit format where the least significant bit is the read / write bit.

5

I'm completerly new in this kind of data transmission.
I'm using a code written for SPI that I found on Internet. It works with a MMA7455L accelerometer mounted on a PCB with 3 pins availables, but I have 2 pins only.
Therefore I'm sure that the code is correct (for 3 wires at least).
Right now I'm not able to write a code for this application, and hence the question.

Thanks

6

You can't do true bidirectional SPI with less than 4 wires.

You can't do Freescale's 3 wire they-call-it-SPI-but-it's-not-reallly-SPI with less than 3 wires.

-j