Z80 Demo Board with "Woven-Wire" Read-Only Memory

Hi everyone,

I'm stepping out of my usual "Apple-1" subforum because I'd like to share my latest educational/informational project, which also ended up on hackaday.com:

https://hackaday.com/2024/10/16/diy-core-rope-memory-z80-demonstrator-generating-a-fibonacci-sequence/

It is a Z80-based Demo Board, which calculates the first numbers of the Fibonacci sequence (at least the two-digit ones!).

The peculiarity of this board is that the program code is stored in a "Woven-Wire" Read-Only memory.

This kind of memory, dating back to the 1950s/60s, is also called "transformer" memory and is a closely related to the well-known "Core Rope" Read-Only memory used by NASA for lunar missions (see AGC - Apollo Guidance Computer).

"Woven-Wire" and the "Core Rope" are often confused with each other -especially in some internet videos- because of the appearance of "many wires going in and out of ferrites", however the "Core Rope" is much more

complex and sophisticated than the one I built.

Both are not to be confused with "classic" magnetic core memories (which are rewritable) -the functioning principles are in fact completely different:

Magnetic core memories:

- 1-bit capacity per core, rewritable, the information is contained in the state/verse of magnetization of the ferrite.

"Woven Wire" memories:

- capacity of many bits per core (16, in my implementation), the information is contained in the wiring itself and not in the state/verse of the magnetization, so it is "Read-Only by design."

"Core Rope" memories:

- capacity of many bits per core (up to 192 in the AGC), the information is contained both in the wiring of the wires that are "activated" when needed, and in the magnetization. Also this is "Read-Only by design."

In the video I have put a brief -but hopefully clear- summary on how the "Woven-Wire" works.

I hope to bring the board to some next exhibition, and be able to narrate the functioning of this forgotten but fascinating technology.

I would like to publicly thank the  Retrocampus  team for the support during the debug, and especially Alessandro Breschi  for writing the program for Fibonacci in no time -and exactly 16 bytes long!

Documentation and schematics are available at the link to my GitHub repository:

https://p-l4b.github.io/corerope/

I anticipate that in the design I took many liberties (some of them questionable) but the goal was also to reuse components I had at home.

I hope I have summarized/justified them in the reference document.

Happy viewing! :-)

https://www.youtube.com/watch?v=26skBvMBiA4

board.jpg

Cheers,

Claudio - P-LAB