{61} Reverse Engineering a Z80 based, 1980 Miller Technology M-80 Single Board Computer

The z80 based Miller Technology M-80 Single Board Computer appeared on the scene in 1979 or 1980 and was available as either a bare board, a kit, or fully assembled. Magazine reader inquiry briefs indicated the board has 2K of 2708 EPROM and 2.1K of RAM, 16 I/O lines with a standard sized 2x22 card edge connector. The I/O was provided by a National Semiconductor’s INS8154 which provided 128 bytes of RAM as well as two 8-bit I/O ports. Port A of the 8154 has a four modes including strobed handshaking, tri-state, and basic I/O. Basic I/O includes both byte handling and a simple and efficient bitwise set/clear operation. I have been unable to find any documentation for this board beyond these short product introduction announcements, so this video shows my reverse engineering techniques to learn the bare basics of how the board works and, specifically, how the I/O port is addressed. Hopefully, someday the schematic and additional documentation for this board will appear, but for now it deserves at least this moment of fame and effort.