The Main Computer is a low power single board computer with several specialized features. It was designed to be the control computer of the Gemini robot. It is a low power CMOS design with a 4 MHZ 8 bit Rockwell 6502 CPU.

It has a real time clock, 8 channel a/d converter, 5 serial ports, a parallel printer port, a bi-directional parallel port, 16 bit I/O ports, a hardware random number generator and a ROM monitor.

It also had four expansion slots that were similar to the slots of an Apple II computer of the time. Some of the expansion boards for the Apple would also work in this computer.

A ROM expansion board was available that holds an additional 56K of bank switched ROM. These ROMs hold the Gemini "Life Mode Operating System" which includes a scheduler, voice command system, Robot BASIC programming language and an extensive vocabulary of compressed speech.

A parallel interface board was also available. This board was designed to add an additional 16 I/O bits.

Here is a complete schematic of this board broken into 3 pages. main1.pdf, main2.pdf and main3.pdf.

Here is a picture of the main computer printed circuit board.

Here is the ROM expansion board. It holds seven 8K byte memory chips.