AVR-Chat

On Thursday 07 September 2006 09:47, OWEN-A wrote:
> I know this is perhaps a bit off topic but I have several boards with
> PIC16F877 processors driving an HC595 shift register and the output pins
> from the pic driving the HC595 are virtually all glitches.

If you are trying to cascade 595's watch the setup&hold time from the Hq' output
to the rising edge of the clock.  The 595 clock on the wrong edge when used
in a cascade, causing a race condition.  If you are bit-banging some pins watch
for this race as well.  The internal I/O clock synchronization of the PIC and AVR
I/O can mislead you, when it comes to setup&hold issues driving clocked logic,
if you are not aware of the internal operation of the I/O.


The TPIC6595 clocks on the falling edge so they cascade safely.
http://focus.ti.com/docs/prod/folders/print/tpic6595.html
Note that the 6595 is a five volt only part unfortunately.
There are also the TPIC6/a/b/c/595 parts.

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