topic SPI: SCK input too sensitive? in S12 / MagniV Microcontrollers

SPI: SCK input too sensitive?

pittbull — Wed, 26 Apr 2006 16:13:05 GMT

Hello,
I'm using the SPI (slave mode) of an S12XA256 to sample serial data from another device (clock frequency is ~500kHz). At roughly 1..2-hourly intervals there seems to be a glitch on SCK that disturbs SPI and shifts in an additional bit. How can I get rid of that? I fiddled around with low-pass filters but it doesn't work until now...

Anyone can help?
Thanks in advance,
pittbull

Message Edited by pittbull on 04-26-200604:13 AM

Re: SPI: SCK input too sensitive?

rocco — Thu, 27 Apr 2006 01:20:14 GMT

Hi, pittbull:

An intermittent that happen every few hours will be a pain to find. I would try to find the source of the glitch, and attack it at the source.

What is the source of the clock? Could some event be causing it to glitch? I have found these problems hard to deal with without using ~SlaveSelect, but easy with ~SlaveSelect.

Nowadays, whenever I use the SPI in slave mode, I bring ~SS high when the SPI is idle. That will re-synchronize the SPI clock if it does get in trouble. If the glitch occurs outside of a transfer, it will be ignored if ~SS is high.

Hope it helps . . .

Re: SPI: SCK input too sensitive?

pittbull — Thu, 27 Apr 2006 15:25:43 GMT

Hello rocco,

Thanks for the reply.
The clock source is a sensor with an SPI-like interface (called SSI). Meanwhile, I replaced the sensor with another S12X module which simulates SPI using I/O ports and always send the same data word. And - surprisingly - the misfeature still exists!

There must be another problem. Probably the supply voltage collapses for a very short time or something like that.

Thanks again,
pittbull