Memopak Centronics Interface, plus another.

ZX80 / ZX81 hardware and software offered for sale or swapping
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Erm
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Memopak Centronics Interface, plus another.

Post by Erm »

Hello.

For sale here is a Memotek I/F Centronics Type Parallel Printer Interface plus what looks to be a home/kit made Centronics Interface of some kind.

The Memotek device: is in excellent condition, gorgeous satin black metal with hardly a mark on it. The PCB inside also looks great. I don't have the cable that goes with it, nor do I have a Centronics printer so to test it I plugged it in to a bog standard ZX81 and it booted as normal. I was then able to Peek the addresses of the Memotek ROM (2800h to 2A00h) and those addresses certainly read differently compared to when the interface is not attached (e.g.10240 is 32 with it plugged in and 24 without it). So it's certainly 'there'.

The other device: appears to be home-made, but perhaps from some kind of kit as the PCB has 'Centronics' written on it and was certainly designed for a ZX81. The ZX81 expansion plug appears to have been sourced from a ZX Printer. It has 3x 74X chips on on the other end is a Centronics type connector. The ribbon to this connector has 3 wires that were either never connected or have become unattached - I think I can make out where 2 of them were once soldered and the 3rd is a mystery.

£70 plus postage (for both devices).
20200920_212829_resized.jpg
20200920_212848_resized.jpg
20200920_212909_resized.jpg
20200920_212927_resized.jpg
20200920_212945_resized.jpg
I'm Chris, a Brit in Germany (Chr$ on the QL forum). https:\\QXL.WIN < QL related collection.
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Erm
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Re: Memopak Centronics Interface, plus another.

Post by Erm »

Pics of the other device.
20200920_213000_resized.jpg
20200920_213031_resized.jpg
20200920_213046_resized.jpg
I'm Chris, a Brit in Germany (Chr$ on the QL forum). https:\\QXL.WIN < QL related collection.
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XavSnap
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Re: Memopak Centronics Interface, plus another.

Post by XavSnap »

Hi,
If anyone can dump the Zx81 Monitor rom with the If expansion board, i will able to rebuild the original ROM !
The existing Rom is a dump from 2800h to 2A00h, but a part of this Rom is redirected to the $0000-$2000 (?) address to intercept the LPRINT command, like the G007 HR card.
I don't know where is located this memory segment…

I had to code an asm program to compare the original BIOS (in a REM) and the tweaked address relocation…

Tools:
Rom_Compare.zip
(412.09 KiB) Downloaded 256 times
[edit: offset $2000 to $3000 (4096 bytes)]
RomDump.zip
(54.24 KiB) Downloaded 238 times
RUN
SAVE"DUMP"
Last edited by XavSnap on Tue Sep 22, 2020 1:09 am, edited 1 time in total.
Xavier ...on the Facebook groupe : "Zx81 France"(fr)
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Erm
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Re: Memopak Centronics Interface, plus another.

Post by Erm »

Ok, I'll load the ROMdump program and see how it goes. I assume it will want to save the result to tape? Or is the dump and comparison all done on the ZX81?
I'm Chris, a Brit in Germany (Chr$ on the QL forum). https:\\QXL.WIN < QL related collection.
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XavSnap
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Re: Memopak Centronics Interface, plus another.

Post by XavSnap »

Thanks Erm,

The RomCheck tool is an ASM program how read the original BIOS datas from a REM and get ROM BIOS.
It will give you all values/address changed by the If hardware.

The Bios backup retrieve the Bios $0-$2000 and store it in a DIM value.
Run the program and save it as a P file, the Bios will be saved in the Vars segment.

With the If card, you can't use the Zxpand, and your had to dump the audio signal with your computer or numérique recorder.
Juste use EO to convert it to a P file, or zip the Wav (22kb,mono,8b).

Your dump will able to use the If expansion with the ZxPand by switching the zx Bios in this card.

Thanks again.
Xavier ...on the Facebook groupe : "Zx81 France"(fr)
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Erm
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Re: Memopak Centronics Interface, plus another.

Post by Erm »

Doing it now...

When I load the ROM compare prog I get this screen:
20200921_212016_resized.jpg
Doing the dump program now...
I'm Chris, a Brit in Germany (Chr$ on the QL forum). https:\\QXL.WIN < QL related collection.
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Erm
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Re: Memopak Centronics Interface, plus another.

Post by Erm »

Ok, I loaded the dump program and it reported 0/0.

I then did SAVE "DUMP" and recorded the result with Audacity (the zeddy I'm using has a beefed up output so the data looks great). I'm just about to email you the zipped .wav, which is just over 7mb.

Is that all you need?
I'm Chris, a Brit in Germany (Chr$ on the QL forum). https:\\QXL.WIN < QL related collection.
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XavSnap
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Re: Memopak Centronics Interface, plus another.

Post by XavSnap »

Hi Erm,

I'm sorry, i put the wrong dump program !
It dumped the $2000 to $3000 memory segment…

The right program will (REALLY) scan the 0-2000 memory offset.
P & Wav:
BiosDump.zip
(5.86 KiB) Downloaded 211 times
LOAD it, and wait the "9/4" (STOP AT LINE 4)
And Save it (SAVE"DUMP")

Your previous wav was clean and working.
I'm sorry again…
:oops:

You also can display the address from 2166 to ??? and take pictures
10 FOR A=2166 TO 2400
20 PRINT PEEK(A);"-";
30 NEXT A
Change A to avoid the 5/20 (can't display…), or type CLS, CONT (it will work, it's a Basic program!)
listing.jpg
listing.jpg (57.27 KiB) Viewed 5531 times
Spot to list it if the values are the same as the previous listing.

But, the first process will be better, and is working...
Xavier ...on the Facebook groupe : "Zx81 France"(fr)
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XavSnap
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Re: Memopak Centronics Interface, plus another.

Post by XavSnap »

Hi,
I typed the bytes display with the BIOS compare tool.

Original ROM, with its zero bytes readable in the bios:
Capture_ifrom1.JPG
Typed bytes read from the BIOS memory bloc.(hardware relocation)
Capture_ifrom2.JPG
62 bytes misted in the dumped Rom...
Capture_ifrom3.JPG
Xavier ...on the Facebook groupe : "Zx81 France"(fr)
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Erm
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Re: Memopak Centronics Interface, plus another.

Post by Erm »

Just about to email you the new version...

Let me know how that is.
I'm Chris, a Brit in Germany (Chr$ on the QL forum). https:\\QXL.WIN < QL related collection.
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