MCU used in OBD0 MPFI ECUs that has 16k on-chip code memory. Usually copy protected, but there are Mcu Readers. It is mostly 8051 compatible, and features a third timer like many other replacements. The main difference from a pure 8051 revolves around how the A5 instruction is handled.

Can be replaced by a Intel8051-compatible MCU iff A5-free code is used. There are MANY 8051 compatible ECUs, and many of them are also in the same 40PDIP package as the 83C154, making replacing the MCU very easy. The Dallas 80C320, ATMEL 89C55, T89C51RD2 have all been tested by me (Dave).