EightRom by Revaldinho thread

[SerErris]

Hi, I am sure you all know the great modules from @revaldinho
I built myself a EightRom because I could get my hands on all the required parts. In todays world this is a problem after all.

One thing I recognized is, that there is another EEPROM you can use, that is pin compatible with the 27C256 EPROMs.

You can use SST 27SF256 as well and if you have the typical TL866 II programmer you can also program and erase them.

Those EEPROMS are available as used from aliexpress (yes sold as new .. but really are not) for pretty cheap price:
https://de.aliexpress.com/item/1005003595737186.html?spm=a2g0o.productlist.0.0.5cfe399emXq4C0&algo_pvid=140c30c4-8f1e-42a6-ab12-c1f45ad587eb&algo_exp_id=140c30c4-8f1e-42a6-ab12-c1f45ad587eb-1&pdp_ext_f=%7B%22sku_id%22%3A%2212000026424928303%22%7D&pdp_pi=-1%3B8.94%3B-1%3B640%40salePrice%3BEUR%3Bsearch-mainSearch

This is as the time of writing 10 pieces for 8,94 € ... so below 1€ per piece.

I ordered 10 of them and checked them. All of them working and having code in them ;-) ...



The good thing of those chips are, that they were pretty much socketed everywhere and therefore could be extracted without applying heat.

Here is the datasheet if you need it:
https://pdf.dzsc.com/88889/244.pdf

Also please be aware that you need the SF version. Only this is compatible with 5V levels. The VF would be 2.7V levels.

If you want to use the 27SF256 in the EightRom you need to set the 4DIP selector to EPROM.

@revaldinho I did a reverse engineering of the Schematics form the verilog file in Kicad. You did not publish the schematics (not sure if you ever created one for yourself). I found the schematic helpful for me to learn how it works (the hardware logic part of things)

Can I post the schematic here? It is formally a reverse engineering of your work, so better to ask before posting it.

Also I like to make a modified version with a GAL to play around with it (for my own purpose of now). My aim is to create a version that also has a slot for a lower ROM (e.g. diagnostics or CPC464 ROM replacement).

[revaldinho]

@revaldinho I did a reverse engineering of the Schematics form the verilog file in Kicad. You did not publish the schematics (not sure if you ever created one for yourself). I found the schematic helpful for me to learn how it works (the hardware logic part of things)

Can I post the schematic here? It is formally a reverse engineering of your work, so better to ask before posting it.

Yes, it all open source under the GPL so if you want to publish a KiCAD schematic based on it please go ahead. If you've had a board made up and tested from the KiCAD data then I'd be happy to include it in the repository.

All the source for my projects is included, but as I said in the other thread the source for my boards is a text (Verilog like) netlist rather than a schematic. There is a README which takes this plus an additional footer file with library, component placement and prerouting information, runs them through the netlister.py program and generates an Eagle board .scr file. Loading the .scr file into the Eagle board editor builds the board directly without needing to have a conventional schematic.

I have wondered about porting netlister.py to KiCAD, because although the freeware Eagle is very good it can be a bit limiting with only 2 layers and a size limit of 80x100mm. There used to be a kind of hobbyist version of Eagle you could pay for which allowed 4 layers and either a double or quadruple sized board ... but now AutoDesk seem to want you to pay about £500 a year for anything other than the freeware version. Seems a bit of a dead end for hobbyists. Anyway, at some point I will get round to it.

Thanks for the tip on the 27SF256 parts too. I haven't come across these before but they look like a good replacement for EPROMs in this and other retro projects.

[SerErris]

I have the schematic nearly ready .. missing the eproms currently. Then I need to create a PCB from it. However I think it is not really required to have another PCB, your version just works. 

I would actually use it to check on a GAL version of it, so to reduce the size of the overall module - makes it simpler to solder, alot of less pins (hopefully). 

I do have some GALs laying around. but that is also a sourcing problem nowadays. I think 5V is just getting out of fashion after some 30+ years 

[Rabs]

Next project for me is the CPC Eightrom card. Guess this will be another learning experience.   

I have built the old school 512K RAM expansion card and had loads of fun.

So any hints or tips before I start. Keep in mind I have never programmed an EPROM before. Can anyone recommend an EPROM programmer?

[revaldinho]

So any hints or tips before I start. Keep in mind I have never programmed an EPROM before. Can anyone recommend an EPROM programmer?

There are some positive comments on the cheap and readily available TL866 programmers in this thread answering the same question over on StarDot. I haven't used the TL866 myself. I have an old Dataman S4 which is very good, but I was lucky to get a cheap 'untested' (ie not working) one which was easily revived with a new battery pack and some contact cleaner on the pot controlling the display contrast. The S4 and even older S3 are relatively expensive in the s/h market though.

I have mainly used 28C256 EEPROMs rather than EPROMs, since they are electrically eraseable - no need to have a UV eraser. I think these EEPROMs may be out of production now (all 5V through hole parts seem to be slipping away) but the 27SF256 parts recommended above look like a good alternative. Still, summer is arriving in the UK so if you want to do some cheap UV erasing of real EPROMs you just need a bit of patience. I did some experiments once to see how quickly you could erase EPROMs by just leaving them in the sun. Two weeks did it for the oldest EPROMs, but just a few days was enough for some of the newer ones with lower programming voltages.

 

[eto]

I just recently bought a TL866 based device. It works well. I don't really trust the Windows software, so I installed it on an old Laptop I don't use otherwise. 

[revaldinho]

You can use the TL866 with Linux and MacOS using the open source minipro software.

[Rabs]

So any hints or tips before I start. Keep in mind I have never programmed an EPROM before. Can anyone recommend an EPROM programmer?

There are some positive comments on the cheap and readily available TL866 programmers in this thread answering the same question over on StarDot. I haven't used the TL866 myself. I have an old Dataman S4 which is very good, but I was lucky to get a cheap 'untested' (ie not working) one which was easily revived with a new battery pack and some contact cleaner on the pot controlling the display contrast. The S4 and even older S3 are relatively expensive in the s/h market though.

I have mainly used 28C256 EEPROMs rather than EPROMs, since they are electrically eraseable - no need to have a UV eraser. I think these EEPROMs may be out of production now (all 5V through hole parts seem to be slipping away) but the 27SF256 parts recommended above look like a good alternative. Still, summer is arriving in the UK so if you want to do some cheap UV erasing of real EPROMs you just need a bit of patience. I did some experiments once to see how quickly you could erase EPROMs by just leaving them in the sun. Two weeks did it for the oldest EPROMs, but just a few days was enough for some of the newer ones with lower programming voltages.

 

Great thanks, everything ordered, should begin the build next week.

[Rabs]

Got the TL866 II plus, works a charm, checked that all the ICs work and read an 28C256 EEPROM. Programming next  

[Rabs]

It worked, the ROM board is alive. 

I have a working diagnostics ROM now.

Thanks for the help, not had this much fun in ages.

Need to think of another useful ROM, I like programming more than games. Any suggestions?

[revaldinho]

It worked, the ROM board is alive. 

Need to think of another useful ROM, I like programming more than games. Any suggestions?

That's great to hear.

Arnor's Maxam assembler/disassembler is an obvious ROM choice, but for something a bit different I'd say try their BCPL system. 

[GUNHED]

A nice list of ROMs can be found here:
https://www.cpcwiki.eu/index.php/ROM_List

What's about a 4 MB ROM expansion, using 512 KB ROMs (27C4001, the same type being used in Cartridges) for example?
 
No conventional ROM expansion provides more than 2 MB (SF3), usually only 0,5 MB (not much!).
 
Or course it would be even cooler to have a 4 MB ROM expansion using Flash/S-RAM, this way it could be used as ROM disc.

[Rabs]

So in the end I have gone for;

Amstrad Diagnostic ROM
BCPL
FutureOS
Maxam
Protext

All seems to be working. 

Now the fun starts, trying to use them.

[GUNHED]

Great choice of ROMs :-)

Here is Maxam 1.15, just i case. (Most of the time people use 1.14, but 1.15 is newer. Maxam 1.5 is a different story anyway.)

BTW: Sadly in this forum I can't upload ROMs, so it's a ZIP.

[SerErris]

Oh - late to the show (back) .. I use Maxam 1.5 with Protext ... so what is the problem with 1.5 over 1.14/1.15?