> From the circuitry on the die, this pin appears to be an output. If someone with a 386 chip hooks this pin to an oscilloscope, maybe they will see something interesting.
Would be a fun surprise if the 386 had its own Halt and Catch Fire mode.
It had ICE mode (precursor to SMM, but used for production testing and low-level debugging), and according to this article, the pins were exposed at least on some of the chips you could buy:
>On the standard Intel 80386 DX, asserting the undocumented pin at location B6 will cause the microprocessor to halt emulation and enter ICE mode.
[this is written from an ICE perspective - for "emulation", read "normal operation"]
This mode was introduced in the 80286, but I don't think the pins were exposed except in the special bond-out variant for ICE, and maybe early samples. You can trigger it in software (opcode 0F 04 on the 286, or by enabling a bit in DR7 on the 386), but then the processor disconnects from the bus and you have to reset it.
Would be a fun surprise if the 386 had its own Halt and Catch Fire mode.