IMSAI Replica

IMSAI Replica

The Replica was based around the front panel board designed and produced by Don Caprio. The S100 8080A Cpu board was designed by Josh Bensadon of Toronto Canada. It is connected to a S-100 Bus Console IO Board to provide VGA output. This board was designed by John Monahan of the “” website.

This front panel board is designed to be a shoe-in replacement for the IMSAI front panel including its hallmark set of switches. As in the case of the IMSAI system, the board allows you to examine RAM, deposit byte(s) in RAM, halt and single step then CPU as well as view the various status and control lines of the S100 Bus.

The 8080A board can be configured as a bus master where the 8080A controls the bus completely or it can be configured in “slave mode” where the 8080A CPU is inactive but the other components on the board are active and available to another CPU on the bus. Note this “slave mode” should not be confused with the normal IEEE-696 definition of the S100 bus in slave mode where two bus CPU’s transfer bus control back and forth between each other with a well defined handshake protocol (often one being a 16 bit CPU).


Slave mode here essentially means a board with the UARTs, the SD card, 8212’s etc being available to another CPU on the bus.

The board also has two connections that hook up correctly to either the Altair or IMSAI front panels. This conveniently allows you to review the CPU’s in action, single step etc.


Stages of my build


Added switches and making bottom of case

Bottom of the case made up and installed power supply’s with the home made front panel

Perspex front panel printed and added black vinyl wrap to the red perspex




Finshed unit



The Design Files are -: Link

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