I am working on a circuit that contains CD4043 R/S latch. The design on the breadboard works and everything is great, as soon as the PCB was manufactured and components were soldered, an issue with the latch arose.
I use the switch-button on the SET input to initialize the latch and for the restart. But somehow on the output, I always get 0 with no matter what is on RESET input. The exception is when the button is actually pressed, then I have 5V.
However, as I said before, there were no problems on the breadboard.
What I did, but it doesn't help:
- All the unused latch inputs connected to the ground.
- Decoupling capacitors across VCC and ground.
- The design itself based on logic components. Calculated delay times, there should be still enough time for the latch to recognize 5V from the switch, but it somehow doesn't 'hold' it.
- First used SPDT switch, then replaced it with single pole switch + resistor, to avoid open circuit state at the moment of switch.
Nothing has helped :'( :'( :'(
Please advice. If you need extra details I am ready to provide.
EDIT 2: I need the latch output to depend not only on the input signals (A and B in U3), but also on its own output, i.e. if at least one of the input signals is off, the latch goes to 0. As soon as input signals are back, the latch should stay in 0 state until it's initialized with the switch S1.