I have, for the past year or two, been fooling, occasionally, with the DS89C4x0 series MCU's. As part of that effort, I built a little circuit that has a couple of external memory IC's an AC latch to demux the data and address bus, an external 32Kx8 EPROM (actually a BBRAM) and a 32Kx8 SRAM. THe thing is presently set up to use external memory only.

This thing uses an external oscillator rather than a crystal, though the rate I'm presently using is the old-standard 11.0592 MHz clock.

What I did, however, and just because I use this circuit in external memory mode only, was to plug in a few old, Old, OLD, Intel and AMD (1980 or so) MCU's (8751)I ran into on a shelf in the store room. What I found was that these guys, all standard 12 MHz parts, don't do anything, except get really hot, when plugged into the circuit where the DS89C4x0's operate just fine.

What am I missing here? What reason would justify this behavior? All the components aside from the MCU are CMOS.

RE