Something else to be aware of, glitches on the data pins going to the shift registers don't matter at all, unless they are accompanied by a transition on the clock line. Those glitches may be intentional, driving something else. They may be intentional, just to confuse reverse engineers. They may be bugs. Hard to see without a schematic. [Non-text portions of this message have been removed]
Message
Re: [AVR-Chat] OT HC595 AND PIC GLITCHES
2006-09-07 by David VanHorn