Beginners SPI questions

[Dany]

Hi, the explanation in the compiler's library help is rather basic regarding what exactly the SPI read and write functions do.

I understand (from other sources) that SPI does simultaneously sends and receives a byte. Together with what I find in mE's help I can assume the following:

function Spi_Read(buffer : byte) : byte;
- Returns the received data.
- Provides clock by sending buffer and receives data at the end of period.

Code: Select all

take := Spi_Read(buffer);

Writes "buffer" to the SPI device and receives at the same time "take" from the SPI device.

procedure Spi_Write(data : byte) : byte;
Returns Nothing.
Writes byte data to SSPBUF, and immediately starts the transmission.

Writes "buffer" to the SPI device and ignores data received.

My actual question is: are above assumptions about mE's SPI library correct?

I do ask this question because I am a complete novice regarding SPI usage, and I try to understand the usage of the library functions before attempting using them...

[yo2lio]

The SPI is very very simple ...

Take a look at my spi routine , I use this for read and write ...

Code: Select all

function Spi_Read_(dat_in : byte) : byte;
begin
  SSPBUF := dat_in;
  asm
    nop
    movf SSPSTAT,w
    btfss WREG,0
    bra	$-2
  end;
  result := SSPBUF;
end;

[Dany]

Thanks Florin. Do you suggest I use your routine in stead of mE's?

As I assumed (and your routine suggests) the read and write take indeed place at the same time. "dat_in" is sent to the SPI slave and the what is coming from the SPI slave is put in the function result. All is clear now. Thanks!

[yo2lio]

Do you suggest I use your routine in stead of mE's?

No, you can use any routine, I show you how this it's made ...

[Dany]

Thanks Florin!