I'm struggling with a SN74HC595 shift register. Output Qa turns on momentarily regardless of what it is commanded to do, when the OE (output enable) is pulled low. Am I interpreting this correctly that, regardless of anything else, Qa will momentarily go high when OE is pulled to ground based on the timing diagram on page 7 of the spec sheet?
It shows all other outputs will stay low.
Thank you.
Thank you for the clarification. That makes sense.
It's weird, we're getting Qa going high by itself and it corresponds with the /OE pin being set low (I think it's active low) through an Espressis ESP-32-Wrover microprocessor. I've verified that the output enable is getting a solid ground. The blip is lasing for about 800mS, which seems very long in the scheme of things.
Green line = the OE pin on the shift register. The little initial curve is the power supply turning on, then it is pulled up to 3.3V by a 10k pull up resistor. The microprocessor then pulls OE low.
Yellow line is Qa's output. We've set all the register bits to 0 multiple times and this happens almost every time without fail.And some times it's is all outputs that trigger at the same time, but most of the time it's just Qa.
Another older thread here suggested that non-square clock pulses can cause misbehavior. This is my clock pulse:
Admittedly, I do not have the best oscilloscope at my disposal and I probably need to look at this on a tighter time scale and see exactly what it is doing.
