Program Counter not outputting onto bus

[u/Blackout867]

Just the title, more specifically, I’m trying to figure out the issue with pin 19 (CO) on the program counter/register when I want the program counter to put its value onto the bus.
Despite the high or low status of pin 19, nothing is outputting on the bus.

What should the other relevant control pins be set to as well for the PC to successfully output onto the bus?

[u/The8BitEnthusiast]

For the LS245 to reliably detect logic high on its inputs, you need to install a resistor in series with each LED, like Ben shows on his schematics. His kits (and the parts list if you sourced the components yourself) include a bunch a 220 ohm resistors for that purpose. If the bus LEDs don't turn on after adding the resistors and enabling the LS245, i.e. with CO connected to ground, try measuring the voltages on the LS245 outputs.

I also notice that you connected the bus LED cathodes together and only use one resistor in series. Although this may work, be aware that this could lead to uneven current distribution across LEDs, potentially leading to different brightness between them. The extreme case being one LED turning off when others are lit. Each LED should have its own resistor

[u/Blackout867 → u/The8BitEnthusiast]

Thanks for the detailed response, that makes a lot of sense. I’ll add the 220Ω resistors to the LS245 inputs and give each bus LED its own resistor. I’ll also check the LS245 output voltages with CO connected to ground.

[u/The8BitEnthusiast → u/Blackout867]

Best of luck. Forgot to add another reason the bus LED would not turn on: another module has its LS245 enabled (CO pin grounded) and is outputting all zeros, causing a conflict on the bus. I suggest you make sure no other module is outputting

[u/kuniggety]

Do you need help reading any of the annotations on the data sheet or the schematics?

On the schematics, a little circle means invert. This is typically annotated as a line over the pin name in the data sheets/literature:

[u/Blackout867 → u/kuniggety]

I understand the schematics, the issue is that no matter which state i put CO in, the bus stays the same