Why does this circuit even work? - Electronic Circuits Projects Diagrams Free

electronzen · 28th September 2008, 10:58 AM

I made up a little PCB for a rom card that interfaces to a Z80 based SBC.

The problem is, I made a mistake laying out the PCB and didn't connect the ground trace to the flash rom part (AM29F040), its just floating.

The other problem is, the device works _perfectly_.

I'm not an engineer and don't have any formal training in electronics, so its completely puzzling to me why this device should work at all like this.

I tried replacing the AM29f040 with a few parts from other flash makers and they all work too, all with the ground pin floating.

Why does it still work?

Alan

Willbe · 28th September 2008, 04:37 PM

This mistake cancels out some other mistake?

geko · 28th September 2008, 06:44 PM

Probably has some protection on the inputs (diodes) which are allowing low logic levels on the control and address lines to pass to the chips internal Vss plane.

You're operating the device out of spec' and while it may 'work' you want to get some mod wire and get the Vss input connected ground.

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28th September 2008, 10:58 AM	(permalink)
electronzen	Why does this circuit even work? I made up a little PCB for a rom card that interfaces to a Z80 based SBC. The problem is, I made a mistake laying out the PCB and didn't connect the ground trace to the flash rom part (AM29F040), its just floating. The other problem is, the device works _perfectly_. I'm not an engineer and don't have any formal training in electronics, so its completely puzzling to me why this device should work at all like this. I tried replacing the AM29f040 with a few parts from other flash makers and they all work too, all with the ground pin floating. Why does it still work? Alan

28th September 2008, 04:37 PM	(permalink)
Willbe	This mistake cancels out some other mistake?

28th September 2008, 06:44 PM	(permalink)
geko	Probably has some protection on the inputs (diodes) which are allowing low logic levels on the control and address lines to pass to the chips internal Vss plane. You're operating the device out of spec' and while it may 'work' you want to get some mod wire and get the Vss input connected ground. __________________ Pete picprojects.org.uk