20X2 hspi - sdi State

[Solar Mike]

I want to send data to some shift registers using the hspi - sdo pin C.1 on a 20X2 chip, I dont care about the sdi input B.5.

Reading the manual is a rather vague about the subject, saying the sdi port has to be in the correct state in order to send data out, without actually saying what state is needed; the only example is for an EEPROM read\write.

Can anyone tell me what I need to do with the sdi input, do I just ground it or pull it high, or can I ignore it and use it for other purposes.

Cheers
Mike

 

[inglewoodpete]

It's been a while (5 years) since I used the PICAXE's hSPI. I think that Rev-Ed are saying that, if the SPI idle state is configured as idle-low, then the SPI-In pin should be low before starting a transfer (and vice-versa).

Having just said that, I don't recall it having any effect in my project. You might have to test the theory yourself and report back.

As an aside, you can't use a PICAXE SPI in full duplex mode (Shift In and Shift Out in the same transfer) - even if you use PeekSFR and PokeSFR commands. I spent hours trying to make it work before giving up and using a raw PIC and MPLAB X.

 

[Solar Mike]

Thanks, I'm in the middle of designing another pcb with the 20X2, too complex for breadboarding, so I will terminate in a 3-pin link, allowing high or low on the sdi pin.

Cheers
Mike

 

[inglewoodpete]

Thanks, I'm in the middle of designing another pcb with the 20X2, too complex for breadboarding, so I will terminate in a 3-pin link, allowing high or low on the sdi pin.

Cheers
Mike

Breadboarding is still a good idea - just to test the SPI functionality.

You just need the power and download components plus a couple of LEDs with resistors to test the functionality. A few lines of code to initialise the hSPI peripheral and then enter a loop the outputs a few bytes before a longing pause (Eg 2-seconds). If you set the SPI clock speed very low and get the LED polarity correct, you should see the Clock and DO pins flash if they are toggling.