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Memotech MTX ROM & EPROM pin-outs

Posted: 11 May 2013 22:44
by 1024MAK
Memotech MTX ROM & EPROM pin-outs

As information on Mask ROM and PROM chips is hard to find, and as there are a number of different pin-outs for different EPROM chips, I thought I would provide some of the much needed information.

I have attached a zip file containing spreadsheet files (in OpenOffice.org and Excel file types) that compares the different pin-outs of the different chips (both some Mask ROM, some PROM and some EPROM types).
There are three different files. One for 4000-04 boards, one for 4000-05 boards (as these normally use different chips) and a general one. The zip file is called "ROM & EPROM pin-outs.zip"

Code: Select all

Issue 4000-05
=============

Uses three 8k byte Mask ROM chips ("A", "B" and "C").
On the board, they are "hard-wired" as position 'a' of links 1,2,4 and 5 as shown on the schematic diagram.
ROM "C" (position 10H on the board), pin 22 is from the extra 74LS00 (10J).
ROM "B", pin 22 is from the extra 74LS00 (10J).

Issue 4000-04
=============
Uses two ROMs or two EPROMs (one 8k byte and one 16k byte)
See pin-out diagram.
MTX ROM and EPROM notes_4000-04.png
MTX ROM and EPROM notes_4000-04.png (20.73 KiB) Viewed 2869 times

Code: Select all

ROM "A" (position 9H)
Pin 2  Link 5 a  to 0V
            5 b  to A13
            5 c  to A12 (production board setting)

Pin 20 Link 4 ab to A11
            4 c  to /RD (production board setting)

Pin 22 --------- to /CEA  (individual ROM select)

Pin 23 Link 2 ab to A12
            2 c  to A11 (production board setting)

Pin 26 Link 1 ab to +5V
            1 c  to A13 (production board setting)

Pin 27 Link 13 H to +5V (production board setting)
            13 L to 0V

ROM "B" (position 8H)
As for ROM "A" except:
Pin 22 --------- to /CE64B  (individual ROM select)
I hope these are useful. If anyone wants to know more, just ask :mrgreen:

Mark

Edited on 2014-10-14 to add some extra information.

Re: Memotech MTX ROM & EPROM pin-outs

Posted: 22 Sep 2013 11:37
by 1024MAK
While working on a faulty MTX board at Memofest 2013 (yesterday, Saturday 21st September), we were confronted with an unfamiliar EPROM chip.

The chip was type 25P64 as shown in this picture.
MTX EPROM type 25P64
MTX EPROM type 25P64
photo 25P64 (p).JPG (38.77 KiB) Viewed 3164 times
A quick search of the web for the data sheet was unsuccessful. However, a data sheet for a similar EPROM from the same manufacture with a similar part number was found.

A copy is attached.

It should be noted that this EPROM chip is not compatible with a standard MTX board designed to take three 8k x 8 ROM chips, so under a board that has been modified to take this type of EPROM, you will find more of Memotech's yellow wiring...

<picture of underside of the PCB coming soon>

Mark

Re: Memotech MTX ROM & EPROM pin-outs

Posted: 26 Sep 2013 17:22
by 1024MAK
Note that the following images are large.

Modified 3 ROM 4000-05 PCB top
Image

Modified 3 ROM 4000-05 PCB bottom
Image

Modified 3 ROM 4000-05 PCB bottom close-up
Image

If you look carefully you can see some of the track cuts that have been made.

The tracks that have been cut are:
ROM socket pin 2 tracks (top side)
ROM socket pin 22 tracks (both sides)

The yellow wires reroute the Memotech's /CE lines from pin 22 to pin 2 on each ROM socket.
Pins 22 and 27 are connected to pin 14 which is 0V/ground.

Mark

Re: Memotech MTX ROM & EPROM pin-outs

Posted: 09 Jan 2020 13:32
by o0Nosferatuo0
Hi, i have a 4000-04 board and i would like to know if i can use Eproms as is without any modification?. I would be using a 27C64(8k) and a 27c128(16k) Eproms.

I've dumped my Roms but i would like to know if someone could send me the UK dump for the 4000-04 so i could compare with mine, to see if everything is ok.

My machine boots to a Black Screen and buzzing noise, but right now has more than 80% socketed ic's. My last will be removing the actual RAM's to see with new ones if i can bring it back to life.

When i press Reset, there's some activity on screen, so i believe it's not totally dead yet.

Best regards,
Pedro Torres

Re: Memotech MTX ROM & EPROM pin-outs

Posted: 09 Jan 2020 14:13
by Dave
Hi Pedro,

those EPROMs sould be OK - this page might help . ..

http://primrosebank.net/computers/mtx/c ... s/roms.htm

(Check the pinning of the links)

I'll try an dig out a copy of the ROMs later, or you could use a Test ROM

regards
Dave

Re: Memotech MTX ROM & EPROM pin-outs

Posted: 09 Jan 2020 14:33
by stephen_usher
I found the Diag ROM image invaluable when diagnosing the problems with my machine, especially as it doesn't need working memory.

Re: Memotech MTX ROM & EPROM pin-outs

Posted: 09 Jan 2020 14:54
by o0Nosferatuo0
Hi and thanks for all the help. Can you point me to the DIAGROM?

Best regards,
Pedro Torres

Re: Memotech MTX ROM & EPROM pin-outs

Posted: 09 Jan 2020 20:17
by Martin A
The diagnostic board / rom has a thread in new hardware at:
http://www.mtxworld.dk/memorum/viewtopic.php?f=17&t=420
The final build of the rom (build 245) is near the end of the 3rd page