SPI communication problem (newbie)

**lm555cn** · - 1st March 2008, 14:58

Thank you very much for your answer falingtrea. I forgot to mention on the first post I'm using PicBasic Pro from microengineering labs with a PIC16F84 and a 10MHz crystal. I'm powering the PIC with 5 volts and the SPI sensor with 3.1 volts. It's still not clear to me if just by using the shiftin and shiftout commands I get the 2KHz that the datasheet specifies for the clock, or if there's a formula on how to calculate that depending on your crystal.

Now, from your reply I believe I have the following:

1) From what I understand the part clocks data in on the falling edge and out on rising edge.
2) The part is unidirectional.
3) I don't know I hope I can use the shiftin and shiftout commands.

I would like to attach part of the datasheet for what we are discussing in case you have some spare time to look at it and are willing to help me in case I'm not explaining myself clear or I'm confusing things, but unfortunately I don't see the option for it.

Kind regards.

**falingtrea** · - 3rd March 2008, 15:23

One thing you should do is preset the CLK and Data lines before calling Shiftout or Shiftin. Just set the clock to output and the correct idle state level, and Data to an input. Some parts could be picky about the starting state before you drop CS. Also, you didn't mention the clock idle state for the part you are using. That is very important also.

I would also just define one data pin variable. Since it is unidirectional, you only have one data pin anyway. Less confusing that way.

And is the output high level of the SPI device high enough for the PIC to accept as a high? The portB pins you are using are TTL and need at least 2V for a high.