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expected 486 bus activity


Experienced Member
Jul 13, 2020

I got a cacheless UM498 with soldered-on 486 CPU.
There is a bodge resistor on the back I didn't notice before with one leg unattached, so I'm unlikely to proceed with trying to fix it further. I looked around for what looked like the place where it got detached from and soldered the leg there but it didn't help.
But... I have a question about what valid bus activity would look like.

Hooking up an oscilloscope on an ISA slot, I see four bytes of activity: ea 5b e0 00, which makes sense as that's the start of a jmp far f000:e05b which is standardized as the POST entry point from ffff0.

The CPU D0 pin goes low and stays low though while A0 is going up and down.
And most of all, the RDY# and BRDY# pins look like they are always low. This points to a failed chipset or a broken component connecting the chipset and CPU?
I should eventually see RDY# go low at the same time as bits are being passed on D0...D31 (I know about the steering issue thus I can't just look at D0...D7 like on the ISA slot) right?