I first ran across the INS8073 inside an RB5X robot when I was a student volunteer at COSI. Much later, the older brother of one of my old COSI Volunteer buddies gave me a small single-board computer because it had some TIL-311 hexadecimal displays (as used on the Quest Elf). I pulled the displays off the daughtercard and tossed the SBC in a drawer, and forgot about it for years. Eventually, I ran across it and for the first time, really looked at it. I was surprised to find an INS8073 in the middle of the board.
A couple of years ago, I started reverse engineering it. After I'd traced most of the circuit, one of my early leads bore fruit - the board was made by BASICON, their "MC-1N". The owner of BASICON sent me scans of the old manual and gave permission to distribute it. It's been OCRed (and spell-checked), and is available as an ASCII file and a PDF.
The MC-1N isn't particularly complicated. The 74S188/82S23 PROM maps 5 address bits (A11-A15) into 8 chip selects, the 6116 on the board, an optional 2716 or 2732 EPROM, selects for SRAMs that aren't available on this board (in 2K increments), the 8255 PPI, and the MM58174 clock/calendar chip. The map looks something like this:
Select Memory Range Destination 01 $2800-$2FFF alt RAM bank 3 (2k) 02 $1000-$17FF onboard 6116 SRAM 03 $A800-$AFFF MM58174 04 $2000-$27FF alt RAM bank 2 (2K) 05 $B800-$BFFF 8255 PPI 06 $8000-$8FFF 2716/2732 EPROM 07 $1800-$1FFF alt RAM bank 1 (2K) 08 $F800-$FFFF Baud Rate Jumpers
Most of this is documented in the manual, but not the alternate RAM selects. Either BASICON had ideas for an expanded product, or they just didn't want to waste 3 outputs of the address select PROM.
The missing 8-pin chip in the picture above is an ICL7660/MAX1044 "Negative Voltage Supply", used to generate -5VDC for the LM358N being used as an RS-232 level shifter. If this were a modern board, it would probably have a MAX232 chip in that corner, doing the same job as both the ICL7660 and the LM358N do in tandem.
If anyone out there with an MC-1N finds this page, feel free to contact me to compare notes, share documentation, etc.
Last modified:
26 August 2006
