Imsai 8080 MIO board question

[wiltors42]

A few years back, I got a IMSAI 8080 computer along with all the basic system boards, dual 8" disk drives, some CP/M and BASIC disks, and two MIO rev. 2 boards, and most of the system manuals. I've tested the system with the example programs that are in the manual and the system seems to work just fine. Using the MIO rev. 2 manual, I set the jumpers to 1200 baud, and I connected the SIO port to the DB25 port coming out the back, the DB25 port to an adapter which turns it into DB9, and then the DB9 is plugged into a USB adapter and is in the back of my PC. Using a serial terminal, I set up a connection to USB-TTY at 1200 baud, no parity. I turn the system and the disk drive on with a CP/M disk in it, and hit run. The computer seems to react to the disk drive being powered up, but nothing at all is displayed on the terminal. Can somebody help me troubleshoot my system so I can get the IMSAI up and running?

 

[cosam]

Using the MIO rev. 2 manual, I set the jumpers to 1200 baud, and I connected the SIO port to the DB25 port coming out the back, the DB25 port to an adapter which turns it into DB9, and then the DB9 is plugged into a USB adapter and is in the back of my PC.

Is there a null modem cable anywhere in that lot, or does something else (maybe the USB adapter) swap TX and RX over for you? Might be worth checking your wiring to be sure it's all hooked up correctly. Assuming that checks out, do you have anything with which to look for data coming from the serial port, e.g. a logic probe or scope?

 

[wiltors42]

Well the adapter which changes the DB25 to DB9 is actually a null modem cable. And yeah, I've got the logic probe that actually came with the IMSAI.

 

[cosam]

Any activity on the TX line coming from the IMSAI? If so, trace forwards to check it's getting to the RX pin on the USB adapter.

 

[wiltors42]

Will the IMSAI even be able to load and boot programs off of the disks without some kind of boot-loader being run on the system?