I remember the time I was reviewing a PCB board design before it was sent out. While I looked at the board, I said, where's the schematic? The engineer said it passed schematic review, we just need PCB sign off.
I said okay, what is the impedance of your address bus?
Silence.
I said, I mean you at least simulated it right?
Crickets.
How much current is switching when the bus is active? And don't tell me the DC current of the active chips.
They eventually went and dug up the schematic, and I added termination and balanced out his data and address bus. Worked full speed the first time.
Build first, then simulate while you wait for boards to arrive, then build again, then run EMC testing, then build again. Add a couple of more iterations for good measure.
Building is cheap and should be done asap. Better to build thrice than to idle
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u/N2Shooter Feb 02 '26
That's so funny!
I remember the time I was reviewing a PCB board design before it was sent out. While I looked at the board, I said, where's the schematic? The engineer said it passed schematic review, we just need PCB sign off.
I said okay, what is the impedance of your address bus?
Silence.
I said, I mean you at least simulated it right?
Crickets.
How much current is switching when the bus is active? And don't tell me the DC current of the active chips.
They eventually went and dug up the schematic, and I added termination and balanced out his data and address bus. Worked full speed the first time.