Which EEPROM chip should I get to burn a new ROM?

[MrM]

Hello!

I've been pouring over some of the older threads and have learned a great deal about burning my own ROM's. I have an Oric 1 with a single BASIC v1.0 ROM and would like to try out a few of the other ROM's I see floating around, especially the diagnostics ROM and the Atmos 1.1 ROM. I think I found all the information I need but I'm a bit of a hardware noob (I'm a software guy) so wanted to double-check a few things. It will suck to wait a month for everything to arrive from China only to realize I ordered the wrong parts!

First, I'll be getting a MiniPro TL866 off eBay. There are quite a few sellers on eBay and they seem to all come in the same CS an A model (I'll probably just get the CS model).

Next, the chip itself. This is the part I'm still a bit fuzzy on. From what I gathered an EEPROM is better than an EPROM because I don't have to get the UV eraser. As far as EEPROM's go, it sounds like I need to get a "28C" DIP-28 chip, right? I see a few Atmel's that fit that description on eBay but I'm not 100% sure which one will work for sure. Some of the models are AT28C64B-15PU, AT28C64-15PC, AT28C64-15PI, AT28C256-15PU, etc. Which one of those chips will be best use in the Oric 1, or doesn't it really matter?

Thanks!

[Dbug]

I will let the smart people answer, but I remember having seen some Orics with more than one rom available, using some micro-switches to select them.

If you use a 32KB eprom instead of 16kb, you should be able to have say the ROM 1.0 of the Oric 1 and the ROM 1.1 of the Oric Atmos -which would give you access to most of the available software around.

With a 64KB one, you could have 4 roms, so additionally you could also have the diagnostic rom, the ROM 1.x that somebody made with some bugs fixed and optimized graphic routines, or the "cracking" rom that a CEO member made - which include a debugger and a memory tracer (ROM renifleuse).

[mmu_man]

Indeed in this era EPROM generations mostly had backward compatible pinouts to allow reusing designs, by adding the extra addressing pins at the top of the package. You need to make sure the pinout is compatible by checking the datasheet.
People also did this on Atari ST to get multiple TOS versions:
http://www.tehkella.net/retro/?p=257
http://atari.8bitchip.info/flashest.php
http://forum.atari-home.de/index.php?topic=9665.220

[MrM]

I will let the smart people answer, but I remember having seen some Orics with more than one rom available, using some micro-switches to select them.

Thanks, I remember seeing posts on this topic but if I remember correctly it required some motherboard mods which scares the daylights out of me Or is there a way to have multiple ROM images on one chip and select them during startup?

You need to make sure the pinout is compatible by checking the datasheet.

I actually tried to read the data sheet on some of these chips for sale on eBay and promptly got even more confused about which chips will work

Having said that, I'm pretty sure this one will work. It's a 256K chip so a lot of space will go to waste if I can't figure out the multi-ROM option, but it's dirt cheap!

[iss]

If you decide to use AT28C256-15PU (from your eBay link) just as new single ROM (i.e. without using the available space to have more than one ROM) you have to write data in the second half or simply concatenate twice the ROM image and write it to the whole space. Here I mean you are using 16K bytes long image file.
Second important thing to remember: you will be NOT able to use microdisk controller together with above EEPROM - pin 27 is used to disable the ROM chip and in AT28C256-15PU this is pin has different function (/WE - write enable).
BTW, how many ROM chip(s) are in your Oric (a picture can be answer here too ) ?

[MrM]

Thanks for that information! I will be sure to concatenate the image. I have a single ROM chip. Here's some picture I took of the motherboard:

[iss]

Yes, everything looks fine. One ROM on socket I think there will be no problem.
Get the MiniPro TL866 CS - it work really well (btw, the CS can be hacked to A model, but this is another story ).
Don't forget to post the results here.

[MrM]

I will definitely post a follow-up. I've learned a lot from the forum so it will be nice to give back!

Items have been ordered ... now for the looooong wait for everything to arrive from China

[Silicebit.]

... Second important thing to remember: you will be NOT able to use microdisk controller together with above EEPROM - pin 27 is used to disable the ROM chip and in AT28C256-15PU this is pin has different function (/WE - write enable)....

To use Microdisc controller with EPROM or EEPROM you can use this invention . http://retrowiki.es/viewtopic.php?f=7&t=200031702