Sinclair ZX80 / ZX81 / Z88 Forums

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).

Pics of the other device.

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: [edit: offset $2000 to $3000 (4096 bytes)] RUN
SAVE"DUMP"

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?

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.

Doing it now...

When I load the ROM compare prog I get this screen: Doing the dump program now...

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?

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: 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…


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!)
Spot to list it if the values are the same as the previous listing.

But, the first process will be better, and is working...

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

Original ROM, with its zero bytes readable in the bios: Typed bytes read from the BIOS memory bloc.(hardware relocation) 62 bytes misted in the dumped Rom...

Just about to email you the new version...

Let me know how that is.