I'm software, not hardware, and would ask our electronics guy, but he's away on a site visit. Someone on StackOverflow suggested I repost this here.
I get the basic idea of a pull up resistor as explained on the first few links Google throws up, but as they're used in the circuit diagram I'm looking at I'm not 100% sure. The examples I've seen all show them used along side a switch that closes to ground, so they hold the voltage up until the switch is closed. Fair enough. But here I have not a switch but the output from a flip-flop latch.
Now, when the output from the latch is low/zero, is that the same as ground? I hadn't thought so, but I don't see how else the input at the other end would otherwise ever be taken low...
VCC | | PULL UP RESISTOR | | \|/ LATCH OUTPUT ---->---------> ON/OFF INPUT FOR OTHER COMPONENT, ACTIVE HIGH
Apologies for the ASCII circuit diagram...
So assuming VCC is always on, how is the component ever switched off? The only way I can think is that the latch output being low is equal to it being a ground, but I'm not sure that's the case.
The latch component is 74AHC574 (it comes straight up on Google).
This started out as a software investigation, but we're not sure the component on the right is being power cycled as the code suggests.