More digging later has revealed three Usenet articles from the same week in 1997 of a product called the "BASICON MC-1N REV A" - there's no vendor name on my INS8073 board, but the part number matches. The Basicon, Inc. website says they are the victim of the current economic times. I've written the repair service listed on their page, but we'll see if they answer. In the meantime, has anyone heard of Basicon? Might their "MC-1N" be the same as what I have (INS8073, 2K SRAM, 8255...)? I've figured out most of the circuit - what has me stumped is that the chip selects are all run through a 74S188 burned as an adress PROM (its address lines are attached to A15-A11 of the CPU, and its data lines go to various chip selects on the board). I've tried building a circuit to manually dump the PROM (it's only 32x8), but no success there - all the bits read '0', which means "always selected" for all devices... clearly not correct. Once I figure out where in memory the MM58174A and 8255 are, I can do more than enter simple BASIC programs. I'd like to see if there's room in the memory map to add more SRAM - there's stuff I'd like to port from my collection of PET programs that would need more than 2K (especially since the 8073 doesn't appear to tokenize its BASIC code when it stores it in RAM or ROM). I've tried writing a program to read every Nth location between the top of RAM and the top of memory space (the RAM, I've already proven, is at the standard address of $1000)... because of the way the INS8073 determines its baud rate (110 bps in this case :-P), "empty" locations read back "182" - no matter where I look, though, I can't get any locations outside of RAM space to answer back with anything else. I'd love to get a manual for this, but there just doesn't seem to be that much information on the 'net about it (if I _have_ that particular product). I'm hoping that it is one of these... it's a pretty neat board... 24 I/O lines out the front, 2K of SRAM and either 2K or 4K (2716 or 2732) of ROM and a clock/calendar. There's even optional battery-backup for the clock chip and the SRAM (just add 3V-5V to a particular pin on the serial/power connector). Thanks for any leads. -ethan -- Ethan Dicks, A-130-S Current South Pole Weather at 25-Apr-2004 10:10 Z South Pole Station PSC 468 Box 400 Temp -60.3 F (-51.3 C) Windchill -114 F (-81.09 C) APO AP 96598 Wind 13.3 kts Grid 004 Barometer 685.5 mb (10420. ft) Ethan.Dicks(a)amanda.spole.gov http://penguincentral.com/penguincentral.html