OKI Intel M85C154 Piggyback Microcontroller  
Written by AnubisTTP on 2017-02-05  


The Intel M85C154 is a special class of microprocessor known as a 'piggyback' CPU. Piggyback microprocessors are designed to act as a programming development tool and can be easily recognized by the presence of a top mounted socket. In use, the engineer would program a blank EPROM on a desktop computer with their test code, then insert the EPROM into the socket on the microprocessor so the code loaded inside could be tested. Once the code was tested and finalized, a cheaper one-time-programmable microprocessor with built in EPROM would be used in the final product.

The M85C154, an 8 bit CPU based on the Intel 8051, is fairly representative of a typical piggyback microcontroller. This device has a maximum clock speed of 22MHz and 16k of onboard ROM space. Additionally, the M85C154 can address up to 64K of program ROM through it's piggyback socket.

OKI Intel M85C154 Datasheet (PDF)


OKI Intel M85C154 piggyback microcontroller, shown with a National Semiconductor EPROM installed in the top socket.

OKI Intel M85C154 pinouts and pin assignments.

OKI Intel M85C154 block diagram.

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