After getting OS9 to boot to the shell on my CMS 9619 SBC, I was hopeful to get the DriveWire module working to load in disk images in a more intuitive way. I don't have an extra RS232 to USB adapter currently available to me, so I tried using a USB to TTL level serial adapter on the board's peripheral port connected to the MC6821 PIA. Using the DriveWire module intended for use with the Tandy CoCo's serial "bit-banger" port (also connected to a MC6821 PIA), I was hopeful that I could get things running. Unfortunately, I am pretty sure I am having some sort of baud rate mis-match. The module issues a single character (probably indicating an INIT), then everything is stuck. I am not totally sure what baud rate I should use since my board is running at 2 MHz, compared the the Coco's 0.89 MHz. I think that is probably a lost cause without significant modifications to the timing in the software. (Actually, 57600*(2/0.895) ≈ 128000, a standard baud rate. I will give this a try...)
Once I get my other RS232 to USB adapter, I should just be able to run it off of the serial port, without any bit-banging related timing issues.
RC2020/04 Wrap-up
So, I am fairly happy with my progress this RetroChallenge, despite having to move to a new house. The extra month certainly helped. I was able to:
- Make some hardware modifications on my CMS 9619 to get enough on-board RAM to run OS9 (Part 1, Part 2)
- Get OS9 booted to the shell on the CMS 9619
- Order my EXORbus backplane card design (Part 1, Part 2).
Once I get the rest of my supplies out of storage, I will get some of the backplanes on tindie for purchase.
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