Suggestion: ROM program by hand

[leonardoelias300]

It would be nice a way to program a machine by hand, I mean, its easy to program an EEPROM by just setting address and data pins and pulsing WRITE pin, so a file with the code and a sbc z80 schematic, a printable txt file with the ROM content will be a great tool. Its easy to solder and long time to write it manually, but it sounds like a best tool to me to start a hand made computer from scratch, since papers can survive very long time.

[ghost]

As a software developer who has only ever assembled systems and never touched a soldering iron I'm uncertain about how the bootstrap problem is addressed.

I picture myself with a z80 CPU in one hand, access to a soldering station, and some code having no idea what to do next. :) Personally, I want to document how to get from where I am (eager to survive and help my fellow survivors with minimal knowledge of hardware and software development skills) to where Virgil wants us to be to make use of the system he's developing. Most likely I'll post the results of this exploration to Medium or some such to help others who find themselves in the same boat.

[f4grx]

Here you are! https://electronicsforu.com/electronics-projects/manual-eprom-programmer

That is all is really needed! A high voltage on VPP, switches to set address and data lines, then a programming pulse! And... lots of time and error checking!

This would allow you to "manually punch the eprom tape" :)

It would be better to implement this as a Z80 bus attached peripheral, which is in my todo list.

We could also publish the hex disassembly of the ROM as a gerber file, to be PCB engraved in copper and epoxy, this would be much more robust than paper :)

While you are at it, documentation is something you will want to have with you post collapse. However, Medium or any social platform will likely be down.

It would be nice it you could also provide a compact raw text form of your exploration so we can compile a set of "vital" text files to be burned in a data-only EPROM, possiby readable by your machine like a filesystem. I'm currently doing this with the 68hc11 instruction set, and will likely be doing it for 74xx logic chips and usual memories (like RAM, EPROMs, flash, etc).

We could compile it in a repository...

The largest EPROM I know is a DIL32, the 27C080, it has a full 1 MB (8Mbits). https://www.futurlec.com/Datasheet/Memory/27C080.pdf Available on ebay in OTP and UV erasable options.

There is also the 27C040 and its flash equivalent AM29F040, for 512 KB of storage. https://www.ebay.com/itm/AMD-AM29F040B-120PC-DIP-32-4-Megabit-512-K-x-8-Bit-CMOS/123878202651?hash=item1cd7b75d1b:g:WnMAAOSwFJxdWNRP

I initially preferred EPROMS to flashes due to their possible ability to retain programmed bits for 100 years if the cover is protected correctly. But I see that the AM29F040 advertises 20 years at 125 C and 10 years at 150C, which means even longer at room temperature since temperature is the worst that can happen to flash memory retention. https://www.promelec.ru/datasheet/0/d/am29f040b.pdf

[hsoft]

For reference: the subject was briefly discussed in #60

[hsoft]

@f4grx nice links, thanks. (E)EPROM programming knowledge is very important to consolidate. And yes, it's true that many of those UV-erasable EPROM chips are highly scavenge-able. It seems that every BIOS in those old pentium motherboards are on that type of chip. I've never tried reusing any of them, but I should...

[f4grx]

From my own experience scavenging, old motherboards have winbond flash chips in DIL32 or PLCC (with a "decorative only" hologram sticker on it :p )

It is more common to see UVPROMs on add-on boards like VGA or SCSI cards.

[hsoft]

@f4grx Thanks for sharing that kind of information, it's very helpful.