-- ето

The Intel 386EX microprocessor uses the same 32- bit core as that of the standard Intel 386SX microprocessor, with some enhancements to make it suitable for the needs of the embedded market.

The Intel 386EX microprocessor core is fully static, which means that the processor will remain its state even when the incoming clock signal is removed. The Intel 386EX can operate with 3.0V at 16 MHz, 3.3V at 20 MHz, and 5.0V at 25 MHz.

--> ето основные различия процессоров.
МАCО прав, просто перепаианием работоспособности не получитса

source : ssv-embedded.de/ssv/pc104/p8.htm

80386EX Datasheet : intel.com/design/intarch/datashts/27242007.pdf

тут собственно все необходимые даташиты:
x86.org/intel.doc/386manuals.htm