Sometimes it is a bad part… sometimes.

I’ve spent the last few weeks working on my retro pc project. The first step with the 8284 seemed to go well but the trouble began when I tried wiring up the 8088. I wasn’t getting anything remotely close to the expected boot sequence. According to the datasheet and
The 8088 Project Book a few clocks after dropping RESET back to zero, the 8088 should raise ALE after placing 0xFFFF0 on the address lines.

No such luck.

I tried debugging to the best of my limited abilities and could not seem to get the 8088 to behave. I dropped by EEVblog forums to get some help. Turns out those older CPUs were / are pretty sensitive to the clock levels and the 8284 was not producing a valid clock. After a bit more debugging I decided to punt and order a new 8284 — this time from arcadecomponents.com. After the new 8284 arrived, I dropped it in as a replacement for the 8284 from Jameco I previously used. Success! Good looking CLOCK, READY, and RESET signals from the 8284. But still no good ALE, address lines, or boot sequence from the 8088. Tonight I decided to move the 8088 from one breadboard to another and rewire the 8088.

I’m not sure whether it was using the different breadboard or just the rewiring but I was able to get a good boot sequence. Joy! A shot of the signals via an Intronix LogicPort.

Next stop… adding some address decoders, a ROM, and some SRAM.