ZXblast - ZX81 memory extension plus USB

Any discussions related to the creation of new hardware or software for the ZX80 or ZX81
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metalh4mster
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Re: ZXblast - ZX81 memory extension plus USB

Post by metalh4mster »

Hardware reset with switch (cold start)
There is a simple routine inside of ZXblast to detect if the system was rebooted (warm start)
or new powered-up. RAM contents is checked for this purpose. This is not reliable under all
conditions and there might be situations where a warm start is tried but failed to modified RAM
contents not detected by the firmware.
So there is a way to force a cold start while pressing the shift key and reset switch together or
pressing shift key and power-up at the same time (with pressed shift key)
. This way should
bring back the system safely if accidently a warm boot is detected but RAM contents partly
lost.
Did you try that?

Siggi
Thanks Siggi, already tried but seems that something is wrong at CPLD level.

At the time (2021) I tried an in-place upgrade with the USB method: the firmware was sitting at 1.1 04/2017 towards 1.1C but something went wrong. Also tried to re-flash the SST ROM on different versions (1.1,1.1A,1.1B,1.1C...), but nothing comes out (powers up, screen shows video signal, but blank, no text at all). Maybe I ought to make a look with an oscilloscope onto it and check signals on pinouts (no experience yet there but it's a good occasion to go fully in for that).
Last edited by metalh4mster on Thu Jul 04, 2024 6:16 pm, edited 2 times in total.
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mrtinb
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Re: ZXblast - ZX81 memory extension plus USB

Post by mrtinb »

As I understand it:
  • The ROM holds the software that runs on the Z80, which is intercepted when double-shift is pressed on the keyboard.
  • Then there is firmware for the USB-controller.
  • Last there is the configuration of the CPLD, which contains the glue logic that connects everything. (A CPLD is a PCB with ICs and traces, that can be reconfigured.)
So there are 3 different firmwares. I think the ROM firmware is the only one, that can be updated via USB.

I belive the USB controller can be updated with a special programmer connected to a header on the board, and CPLD needs to be removed and programmed with another special programmer.

I believe it was the CPLD i shipped back to PokeMon, for an update.
Martin
https://zx.rtin.be
ZX81, Lambda 8300, Commodore 64, Mac G4 Cube
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metalh4mster
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Re: ZXblast - ZX81 memory extension plus USB

Post by metalh4mster »

mrtinb wrote: Thu Jul 04, 2024 6:14 pm As I understand it:
  • The ROM holds the software that runs on the Z80, which is intercepted when double-shift is pressed on the keyboard.
  • Then there is firmware for the USB-controller.
  • Last there is the configuration of the CPLD, which contains the glue logic that connects everything. (A CPLD is a PCB with ICs and traces, that can reconfigured.)
Curiously, the ZX81 still signals video with the ZXBlast attached, but something might be wrong (a loop within the CPLD programmed logic, or a condition that never meets up and avoids the ROM programming to be executed, with the usual in-screen prompt). Tomorrow we will make a retrocomputing workshop near a computing museum with a lot of tooling available to make diagnostics, etc...

[Update] I reached out Karl this time directly through Ginger Electronic's main e-mail, let's see if he might release the software components under a non-commercial license for the community; this might help out to keep up with bugfixes and further development.
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siggi
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Re: ZXblast - ZX81 memory extension plus USB

Post by siggi »

metalh4mster wrote: Thu Jul 04, 2024 6:22 pm Curiously, the ZX81 still signals video with the ZXBlast attached, but something might be wrong (a loop within the CPLD programmed logic, or a condition that never meets up and avoids the ROM programming to be executed, with the usual in-screen prompt).ent.
Do you have another ZX81? If yes, does it show the same problem?

ZxBlast uses a lot of Z80 signals, no other expansion card uses (like /NMI, /INT, /Clock, /Wait, /Halt, /Reset ...). If one oft them is missing at the edge connector, other (less complex) cards might work, but not ZxBlast...

Siggi
My ZX81 web-server: online since 2007, running since dec. 2020 using ZeddyNet hardware
http://zx81.ddns.net/ZxTeaM
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