EPROM chips for TOS replacement Atari ST

[zChris]

Will 6 of these EPROM chips be suitable for replacing the TOS chips ? https://www.elfa.se/Web/Downloads/_t/ds ... ng_tds.pdf , my atari st have 6 chips for TOS.

As by the other thread i want to get EmuTOS on to the EPROM so it can load the rest of EmuTOS from floppy.

/zChris

[rubber_jonnie]

They should be fine, but I'd advise trying to get a set of 6 EPROMS that are eraseable, because the devices you've specified are OTP and if you flash them wrong, the only thing you can do is bin them.

I test all my ROMs first this way, and whilst it adds a step, it really is worth it. Of course you can use them as ROMs and then erase if you want to use something different later.

[zChris]

I dont understand why there are EEPROM OTP. Arent those called PROM ? Doesnt the E stand for erasable?

/zChris

[rubber_jonnie]

I dont understand why there are EEPROM OTP. Arent those called PROM ? Doesnt the E stand for erasable?

/zChris

As I understand it:

OTP PROM - One time programmable, no coming back if you do it wrong.
EPROM - Erasable Programmable Read Only Memory. Usually erasable with UV light, which is what I tend to use. They are often in ceramic packages which seem to be a bit more robust when it comes to a lot of handling.
EEPROM - Electrically Erasable Programmable Read Only Memory. Erasable using a programmer, no UV required.

In the data sheet you linked to, it is contradictory, and I'm not sure why, as it says EPROM, which you'd expect to be erasable.

I think it is actually a mis-print, because if you look at the right hand side of the first page of the data sheet under the Atmel logo, it specifically says:

"256K (32K x 8)
One-time
Programmable,
Read-only Memory"

In other words, OTP PROM. It also states OTP a couple more times in the first page, hence why I think the use of EPROM is an error.

I've chucked too many OTP PROM chips in the bin because I didn't have an erasable set to test with first, hence my suggestion that you get some.

I know it does add a bit of extra cost and time to what you're doing, as you have to buy EPROMS and OTP PROMS, but if you stuff it up and have to throw the OTP PROMS in the bin, you'll wish you had a test set.

If you get to something like a 27c4096 ROM, they are not cheap, so a test set is a good way to make sure you got it right.

[DoG]

This type of eprom we are using is obsolete technology so you will not find it at Mouser, DigiKey, Farnell or ELFA.

You have to find used part or 'new' old stock.

[tzok]

Technically they are EPROMs, but have no quartz window, so they are called OTP EPROMS.The PROM term seems to be obsolete and reserved, for "fusible" memories.

There is a Flash EPROM replacement for 27C256 - this is Winbond W27C256 (and 27C512). Despite also being 27C marked, they are Flash EPROMS.

[cmorley]

EPROM - Erasable Programmable Read Only Memory. Usually erasable with UV light, which is what I tend to use. They are often in ceramic packages which seem to be a bit more robust when it comes to a lot of handling.

I assumed they never put EPROMs with quartz windows in plastic packages because the UVc would kill the plastic...?

[rubber_jonnie]

EPROM - Erasable Programmable Read Only Memory. Usually erasable with UV light, which is what I tend to use. They are often in ceramic packages which seem to be a bit more robust when it comes to a lot of handling.

I assumed they never put EPROMs with quartz windows in plastic packages because the UVc would kill the plastic...?

If I'm honest I've only ever seen UV erasable devices in ceramic packages, so you're probably right.

[rubber_jonnie]

Technically they are EPROMs, but have no quartz window, so they are called OTP EPROMS.The PROM term seems to be obsolete and reserved, for "fusible" memories.

There is a Flash EPROM replacement for 27C256 - this is Winbond W27C256 (and 27C512). Despite also being 27C marked, they are Flash EPROMS.

Technically, you're right, the chip inside is almost certain the same as the erasable type, it's just annoying when the manufacturer calls them both EPROMS and OTP PROMS on the same page of the data sheet.

The point I was trying to make is that it is useful to have a set of erasable chips to test with before burning to a set of OTP chips.

I always test first before committing to the real thing.

[zChris]

Like these ? https://www.electrokit.com/uploads/prod ... 27c512.pdf

Ceramic and should fit the TOS sockets ?

/zChris