View Single Post
Old 01-05-2009, 05:54 PM
FlashCorliss FlashCorliss is offline
Junior Member
Join Date: Jan 2009
Location: Atlanta, GA
Posts: 4
Default I can't get the Monitor to start...

I got an Altair 680 kit for Christmas from my wife (and Martin). I was very surprised!

However, it was missing all of the sockets, the power cord, fuse holder, back power switch, and most of the parts required to wire up the RS-232 interface. Sadly, I couldn't build it on Christmas day (DigiKey was closed) - Darn.

So, after extravagant overnight shipping, and many hours of meticulous kit building, I was ready to power the 680 up.

LEDs blink, memory can be accessed, read, and written, the power supplies are proper, but I get no "." on the RS-232. The computer is jumpered for 9600 baud, 8, n, 1, terminal, RS-232. The DB25 output (pin-3) shows -12, the input (pin-2) reads close to zero, and ground is ground (pin-7). I connected the DB25 of the Altair 680 to a DB9 for my laptop as so...

DB25 pin 2 - 3 of DB9
3 - 2
7 - 5

I've used several different terminal programs with 3 different laptops, and still no monitor prompt. I'm running with only the 6800 and the ACIA Prom (the memory expansion board and VTL roms have been removed). I have not probed around with a scope yet - was hoping not to. I took the 6850 chip out and jumpered pins 2 and 6 together and I was able to get the laptop to see it's own characters (a loopback through the RS-232 circuit). So I feel confident that the wiring is correct. A logic probes reveals nothing on the output of the 6850 (pin-6).

Any ideas? When the 680 in set to RUN, the upper LEDs (A9-A15) appear to be counting up in binary fashion. In fact, with the ACIA MON rom removed, the A13-A15 LEDs appear to count (I guess it's just random code).

Did everybody else's 680 work okay? What else can I check?

Thanks, Flash

Last edited by FlashCorliss; 01-05-2009 at 07:53 PM.
Reply With Quote