This is probably answered elsewhere but I can't seem to find it.
I have a circuit which uses a Mega8 to drive a couple of ICs as shown in the diagram below.
The ISP connectors in the diagram are: 1: MISO 2: VCC 3: SCK 4: MOSI 5: RESET 6: GND Alse note that the 5V power supply is actually at 4.5V and the ISP's VCC pin is not connected.
I'm seeing the flip-flops being triggered almost randomly. If I connect a resistor between the ICs in series it seems to clean up the signal, and it doesn't matter if the resistor is 10R or 10k. Does this mean that I should always use a resistor when connecting ICs even within the same logic families?
It should also be said I use an STK500s ISP to program the mega8 which means that the circuit ends up with two ground. They seem to be differing about 0.5V. The power supply is at 4.5V so the highest potential is 5V? It's a little unclear to me how these things add up but both the mega8 and the ICs are within normal operating parameters if it's 4 or 5V.
Sorry if it's long winded. I'm not sure how to explain it better. My question concerning this is:
Am I right in thinking the resistor cleans up the signal? And if so how do I figure out the best size for it?
If the mixed ground potential is causing a problem how do I isolate the two ground potentials, since both need to be connected to the mega8 during programming?