A very-vintage (and small) 1960's PROM Diode-Matrix - UK Vintage Radio Repair and Restoration Discussion Forum

ortek_service · 4th Dec 2022, 6:01 pm

With current interest in fusible-link PROM's, I thought this 1960's Radiation Inc. (Before they became Harris) Mil-Spec (and cost?) - I've just had an update the de-capping of about - may be of interest, and it looks to be one of the earliest of this type:

https://twitter.com/TubeTimeUS/statu...12778782588930

Would need quite a few of these to hold even a very basic monitor program etc. so might be more suited for fairly-simple logic substitution with a small look-up table.

TonyDuell · 4th Dec 2022, 6:37 pm

The first of the attached photos shows the bootstrap ROM from my PDP8/e system. The top half of the board is a diode matrix ROM, (a little larger than the one mentioned above) the rest of the board acts like the 'frontpanel' and effectively loads the contents of the ROM into the machine's core memory

The second photo is one of the four core memory planes -- 8192 12-bit words of storage.

ortek_service · 4th Dec 2022, 7:26 pm

Thanks for that - I'd not come across a discrete-diode one before (although I do recall a PW Doorchime project from around 1980, which had a matrix of diodes on a long PCB, to program the tune to be played).

Looking at that PDP-8/e Boot-ROM board, I'm guessing the size was 32 x 12bit Words judging how it is laid-out.

Maarten · 4th Dec 2022, 7:34 pm

Isn't that PDP board a core ROM instead of a diode matrix ROM?

TonyDuell · 5th Dec 2022, 6:06 am

Quote:

Originally Posted by Maarten

Isn't that PDP board a core ROM instead of a diode matrix ROM?

The H212 (second photo) is normal read/write core memory.

The ROM board is certainly a diode matrix. I have the schematics, the technical manual, etc. And yes, I think it is 32 words of 12bits.

I also have, but no photos, the M792 diode matrix boot ROM in one of my PDP11s. That's 32 words of 16 bits and simply appears in the processor address space.

Realtime · 6th Dec 2022, 9:32 am

Any chance you could post the schematics for the diode array? I'm really interested to see what logic overhead was required for that (small) amount of ROM.

SiriusHardware · 6th Dec 2022, 9:51 am

My first foray into CB radio was with a mostly homebrewed setup, and the problem of how to generate the 40 often non-consecutive 9-bit parallel codes for the PLL synthesiser came up. (I didn't have a 40-position channel indicator / encoder switch and saw no way of obtaining one).

I did seriously consider using diodes to generate the codes for every single channel, but then realised they could be supplied from an appropriately programmed EPROM. Not knowing much about EPROMs, I unwittingly bought an expensive 2708 with its nightmarish supply rail requirements for both programming and normal operation. In the end I think I just used a DIP switch for channel selection for a couple of years...

TonyDuell · 6th Dec 2022, 10:09 am

I can't find the MI8E (boottstrap diode matrix ROM) schematics on-line, I should have them on paper but as they're A3 sheets they won't be trivial to scan.

There's a fair amount of nformation including partial schematics and theory of operation in pages 137-153 of volume 2 of the PDP8/e maintenance manual which is avalable from bitsavers in this directory :

http://www.bitsavers.org/pdf/dec/pdp8/pdp8e/

There's a surprising amount of logic on the board, mostly to make it emulate a front panel.

A similar manual for the PDP11 32*16 ROM (which does include schematics) is :

DEC-11-HBMAA-E-D_BM792_Read-only-memory_and_MR11-DB_Bootstrap_Loader_Jan75.pdf

available from here :

http://www.bitsavers.org/pdf/dec/unibus/

DEC were using fusible-link PROM ICs by that point. The reason that the bootstrap roms were diode matrices was that they could be modfied using normal tools (side cutters and a soldering iron), you didn't need aPROM programmer.

4th Dec 2022, 6:01 pm	#1
ortek_service Octode Join Date: May 2018 Location: Northampton, Northamptonshire, UK. Posts: 1,443	A very-vintage (and small) 1960's PROM Diode-Matrix With current interest in fusible-link PROM's, I thought this 1960's Radiation Inc. (Before they became Harris) Mil-Spec (and cost?) - I've just had an update the de-capping of about - may be of interest, and it looks to be one of the earliest of this type: https://twitter.com/TubeTimeUS/statu...12778782588930 Would need quite a few of these to hold even a very basic monitor program etc. so might be more suited for fairly-simple logic substitution with a small look-up table.

4th Dec 2022, 6:37 pm	#2
TonyDuell Dekatron Join Date: Jun 2015 Location: Biggin Hill, London, UK. Posts: 5,224	Re: A very-vintage (and small) 1960's PROM Diode-Matrix The first of the attached photos shows the bootstrap ROM from my PDP8/e system. The top half of the board is a diode matrix ROM, (a little larger than the one mentioned above) the rest of the board acts like the 'frontpanel' and effectively loads the contents of the ROM into the machine's core memory The second photo is one of the four core memory planes -- 8192 12-bit words of storage. Attached Thumbnails

4th Dec 2022, 7:26 pm	#3
ortek_service Octode Join Date: May 2018 Location: Northampton, Northamptonshire, UK. Posts: 1,443	Re: A very-vintage (and small) 1960's PROM Diode-Matrix Thanks for that - I'd not come across a discrete-diode one before (although I do recall a PW Doorchime project from around 1980, which had a matrix of diodes on a long PCB, to program the tune to be played). Looking at that PDP-8/e Boot-ROM board, I'm guessing the size was 32 x 12bit Words judging how it is laid-out.

4th Dec 2022, 7:34 pm	#4
Maarten Dekatron Join Date: Dec 2007 Location: Haarlem, Netherlands Posts: 4,203	Re: A very-vintage (and small) 1960's PROM Diode-Matrix Isn't that PDP board a core ROM instead of a diode matrix ROM?

6th Dec 2022, 9:32 am	#6
Realtime Hexode Join Date: Jan 2021 Location: Ashford, Kent, UK Posts: 318	Re: A very-vintage (and small) 1960's PROM Diode-Matrix Any chance you could post the schematics for the diode array? I'm really interested to see what logic overhead was required for that (small) amount of ROM.

6th Dec 2022, 9:51 am	#7
SiriusHardware Dekatron Join Date: Aug 2011 Location: Newcastle, Tyne and Wear, UK. Posts: 11,586	Re: A very-vintage (and small) 1960's PROM Diode-Matrix My first foray into CB radio was with a mostly homebrewed setup, and the problem of how to generate the 40 often non-consecutive 9-bit parallel codes for the PLL synthesiser came up. (I didn't have a 40-position channel indicator / encoder switch and saw no way of obtaining one). I did seriously consider using diodes to generate the codes for every single channel, but then realised they could be supplied from an appropriately programmed EPROM. Not knowing much about EPROMs, I unwittingly bought an expensive 2708 with its nightmarish supply rail requirements for both programming and normal operation. In the end I think I just used a DIP switch for channel selection for a couple of years...

6th Dec 2022, 10:09 am	#8
TonyDuell Dekatron Join Date: Jun 2015 Location: Biggin Hill, London, UK. Posts: 5,224	Re: A very-vintage (and small) 1960's PROM Diode-Matrix I can't find the MI8E (boottstrap diode matrix ROM) schematics on-line, I should have them on paper but as they're A3 sheets they won't be trivial to scan. There's a fair amount of nformation including partial schematics and theory of operation in pages 137-153 of volume 2 of the PDP8/e maintenance manual which is avalable from bitsavers in this directory : http://www.bitsavers.org/pdf/dec/pdp8/pdp8e/ There's a surprising amount of logic on the board, mostly to make it emulate a front panel. A similar manual for the PDP11 32*16 ROM (which does include schematics) is : DEC-11-HBMAA-E-D_BM792_Read-only-memory_and_MR11-DB_Bootstrap_Loader_Jan75.pdf available from here : http://www.bitsavers.org/pdf/dec/unibus/ DEC were using fusible-link PROM ICs by that point. The reason that the bootstrap roms were diode matrices was that they could be modfied using normal tools (side cutters and a soldering iron), you didn't need aPROM programmer.