Exceltronix Multiflex Super System - page 5 of 5

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Z80 Exceltronix Multiflex Super System (continued)

October 2005: After completing my Exceltronix project and thus getting Geoffrey’s computer running again, the hardware sat around unused. Then, five years later, I wondered if it still ran. I fired it up but it would not boot CP/M. I didn’t have enough interest to find out what the problem was.

February 2006: Geoffrey had health problems later in life and, in February 2006 I learned that he had died at age 86. I will always have fond memories of our working together on various computer projects.

October 2011: Another five years gone by and now twelve years since Geoffrey’s email. Once more I powered up the Exceltronix but it still would not boot CP/M.  I thought about debugging it but decided instead to write a software emulation on the Macintosh. My interest at that time was in using Xcode and Objective-C on the Macintosh and I thought that writing an Exceltronix emulator would be a great challenge and do much to further my expertise. That project ended up taking a couple of months and an account of it can be seen by clicking here.

November 2011: Having written my Exceltronix Multiflex Super System emulator, I found that some programs did not run correctly. I found a program on the Web that would run a test on a Z80 emulator and check that all its Z80 instructions gave the same results as would the hardware (Z80 Exerciser (Zexall/ /Zexdoc)). I found that my emulator failed many of the tests! After much reading and searching the Web, I managed to fix most of them but a few remained. I decided that there was nothing for it but to get the Exceltronix hardware running again so that I could do some tests.

I powered up the Exceltronix with no drives connected. I pressed the BT key but received no boot message on the screen. I tried to use the Exceltronix keypad to go to my serial port test routine at EEPROM address FDE9 but the "9" key on the keypad would not work. I had to unsolder the key from the motherboard, cut it apart, clean the contacts, reassemble it with hot glue and re-solder it to the mother board. Quite a process. It now sometimes sticks, but it does work.

I powered up and used the Exceltronix keypad to run the serial port test routine. By single-stepping I found that characters were being received from the keyboard and were being sent to the screen but they were not arriving. I checked the serial cable and found some errors which I corrected but it still didn't work. I switched from the Macintosh modem port to the printer port and it worked! Maybe the Macintosh modem port is damaged. I pressed BT and the boot message appeared on the screen.

I hooked up the A drive, pushed the BT key and pressed carriage return and the drive light came on. I did a reset, placed a 5-1/4" system diskette in the A drive and repeated the boot sequence. The A drive became active and the CP/M copyright message and A> prompt appeared on the screen. I did a DIR and it worked. Hooray. The Exceltronix lives again! I was then able to use it to run Zexdoc and find the remaining errors in my emulator.

January 2012: I don’t need to run the Exceltronix any more but, just out of interest, I powered it up again. Same old problem of not being able to boot CP/M. I’m sure the problem lies with my aging Macintosh. I don’t think I’m going to be doing any more debugging though. It’s time to move out the old hardware and move on.

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