What would cause a 74hc377 octal D flip-flops to occasionally latch on the falling edge of a clock?

I have several different 74hc chips across several breadboards. I was daisy chaining the breadboard's power lines to distribute power, but this caused the voltage to be inconsistent and certain chips didn't work correctly. So I soldered some wire into a grid and connected the power lines directly to each breadboard. This made every breadboard to have a consistent 5.2 volts, maybe a little high but within spec for all chips. I'm using a cheapo charger power supply if that matters. Anyways, after I did this, the 74hc377 usually works correctly. However, it unpredictably latches a second time at the falling edge of the clock after latching correctly at the rising edge. I don't really see any reason this could happen, so I'm asking here in case I'm missing something obvious. I have decoupling capacitors across every IC (and larger capacitors on the power lines) and all unused input pins are pulled low. I know it's not a bouncing problem, because the push button clock I use is hooked up to a debouncing circuit, and a 555 timer based clock has the same problem. Any ideas?

  • \$\begingroup\$ care to post a schematic and maybe a photo of your work? It could be a layout issue. \$\endgroup\$
    – Aaron
    Feb 3, 2021 at 1:57
  • \$\begingroup\$ Can't right now, I will in a while. \$\endgroup\$
    – bobbbob
    Feb 3, 2021 at 2:00

1 Answer 1


Double clocking can happen if the clock is not clean or has a slow falling edge.

On the negative edge any noise can cause the device to interpret it is another positive edge if there is noise.

This noise could be caused by actual noise, by coupling from other signals or ringing on the clock signal itself. Noise on the ground could also cause a similar effect.

A series resistor at the source of the clock could help reduce ringing. Typically a 33 ohm resistor at the source is used.

Buffering the clock may help if the clock edge is slow.

  • \$\begingroup\$ Would the wire with the clock on it being fairly long cause problems? And how would I buffer the clock? I'm new to electronics. \$\endgroup\$
    – bobbbob
    Feb 3, 2021 at 2:34
  • \$\begingroup\$ Long wires pick up noise, yes. -- You may use a Schmitt-Trigger to buffer the clock, or any unused (non-inverting) gate. But be aware of the propagation delay. \$\endgroup\$ Feb 3, 2021 at 7:49
  • \$\begingroup\$ Sorry I took so long to reply, completely forgot to. Buffering the clock with two Scmitt-Trigger inverters worked. \$\endgroup\$
    – bobbbob
    Mar 5, 2021 at 0:11

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