RC2014 Mini with CP/M upgrade kit not responding to reset button on bank 3
Richard Kiernan
Spencer Owen
Hi Richard,
There is nothing obvious that springs to mind. I would check that the 10k pull-up resistors (R2, R3) are fitted correctly. This should mean that you get a 5v high signal on pin 27 and pin 1 of the ROM (A14 and A15 respectively) with the jumpers removed. Putting one or two of the jumpers on should ground pin 27 and/or pin 1.
The reset signal is also used on the CP/M Upgrade Kit as part of
the ROM paging mechanism to put the counter in to a known state on
start up. It only feeds a NOT gate on the '04 though, so I can't
see how that would be affected by any ROM selection jumpers. But
it might be worth running a continuity check in case there's a
bridged connection somewhere.
Spencer
I've noticed that on my RC2014 Mini, when I have the bank select jumpers removed (therefore selecting Bank 3), the system does not respond to the reset button, whereas the reset button appears to work correctly on the three other banks.This has been an issue for a while, but it emerged at some point after building the kit, as I tested bank 3 when I initially built the system and it was working fine. There have been two physical changes to the CP/M upgrade kit since I initially built it; the two expansion headers and the keyboard passthrough connector were soldered on. As I did not remove the EPROM chip during these soldering operations, I suspected the EPROM may have been damaged in some way, but I've recently acquired a T48 programmer and at the very least, the contents appear to be identical to those of the R0881099.BIN file provided on the RC2014 GitHub page.
Unfortunately, I do not yet have any other EPROMs that have valid data to cover the 0xC000 to 0xFFFF range that Bank 3 covers; I have the R009 EPROM from the Mini base kit, but that doesn't have anything starting at 0xC000. I've given the underside of the boards several good cleans with 99.9% isopropyl alcohol to try to eliminate any electrical interference through flux build-up, although I'm still not ruling this out as a possible cause. While Bank 3 on the R0881099 EPROM is somewhat redundant with the R4 configuration of SCM on Bank 1, I was thinking about writing a custom ROM with Forth on the Bank 3 positions, so it'd be nice if I could resolve it. Is there anything that anybody could think of that I haven't already tried or any points I might need to check with a multimeter?
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Spencer Owen
Hi Richard,
Ok, this has got me scratching my head... but finally I scratched deep enough to understand why it doesn't work.
The ROM image (both the one on GitHub, and my master image (which your ROM was burnt from)) has the wrong value at 0xc001. It is 0x81 and should be 0xBD. I don't know when or how this error crept in, but it looks like it has been there from the first Mini CP/M Upgrade Kits being sold.
So, congratulations on being the first person to report the error :-)
A quick check of the other ROMs and it looks like this is the only one affected. (The Mini II ROM is different to the Mini ROM, and is also unaffected).
I will do a few more tests and upload a new image to GitHub in the next few days.
As you say, this part of the ROM is somewhat redundant, but it *should* work, and I can understand the confusion caused if building the kit and getting no output. So please accept my apologies for that.
Spencer
Hello Spencer,
Thanks for the advice. I've checked pins 27 and 1 and they appear to be feeding the correct 5V high signals corresponding to the ROM positions. I've also done a logic check using the T48 on the '04 and all of the other 74 chips on the Upgrade Kit and they appear to pass.
I've made a couple of other observations:- When using the R0881099 ROM on the base Mini, the corresponding position to Bank 3 on the Upgrade Kit is not working. However, the next bank up (0xE000-0xFFFF) does work and comes up with the expected SCM R1.- The corresponding position to Bank 2 on the Upgrade Kit also doesn't work on the base Mini, but since I expect this is looking for the CF module and it does work on the Upgrade Kit, this isn't particularly concerning.- On the Upgrade Kit, when set to Bank 1 (but no other bank), the A13 line on the ROM seems to be floating, with a voltage of 1.8-2.0V. The voltage on A13 on the ROM, when tested with a multimeter, does occasionally become 0V, but SCM becomes unresponsive at this point and only responds to a reset. The A13 voltage when testing the lower 8KB of this bank on the base Mini is 0V as expected.
I can't tell for sure, but this could still point to a subtle problem with the EPROM, but also to some sort of electrical problem introduced elsewhere subsequent to the initial building of the device.
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