You might have a better time looking for videos on basic 80s computer theory as there were a lot of resources on how they worked and how to even design and build your own comuter (and I don't mean "Assemble your own computer" like you do today from premade parts), but literally design and build your own system, as these computers were really really simple.
and arcade PCB is nothing but a z80 based computer really. believe it or not there's really not much too it
the Z80 MUST have a clock regularly clocking away, otherwise nothing will happen
the other thing is when a game boots up the hardware should trigger a reset
upon receiving a reset signal the Z80 will jump to it's reset interrupt vector (basically a predefined address) and start executing code. This code usually does tests the system and then starts running the code, the reset should only fire once almost immediately after the game is turned on, some older systems have a longer delay until the system PCB detects power is stable. (example, Sega Gremlin dual VIC games)
Without the clock the CPU will do nothing,
without the reset the cpu state will be "random" and the system will not do anything useful. Those really are the only 2 signals that the CPU itself doesn't really initiate.
nothing else should happen when the CPU starts up, at that point you'll start seeing the data and address bus's light up as the CPU starts reading from and writing to memory in accordance to whatever the code says to do.
The other notable inputs to the CPU are often not even connected to anything (just permantely +5)
IRQ - some part of the system wants to interrupt the CPU and cause it to execute a section of code to handle the interrupt. (interrupts can be ignored by the CPU). usually if this is wired to anything this will be wired to a vblank to let the CPU know the screen has been done drawing and restart the main game input loop.
NMI - non maskable interrupts, basically same as above, but cannot be ignored by the CUP
WAIT - basically causes the CPU to well, wait
BUSRQ - requests that the CPU basically stop driving the address and data buses
on the arcade games I can remember I think I've always seen these 3 signals wired to +5 via a pull up resistor so they never are activated
-brian
Are there any videos explaining basic arcade pcb theory?
I have seen Adams video. It is terrific.
But I'm looking for something a little different.
For instance a video that explains a Z80 based arcade pcb.
1: What happens first when power is applied. What signals are sent to the Z80 , what signals aren't.
2: What happens if all the proper signals are present. What's next.
Etc, etc.
Just wondering as I find it interesting.
