nesdev.org

anybody know how you would erase these?

http://cgi.ebay.com/EPROM-ST-NEW-M27C20 ... 3efab3fcca

Some people says that it's possible to erase them with X rays. Personally, I haven't tried that

coinheaven wrote:anybody know how you would erase these?

http://cgi.ebay.com/EPROM-ST-NEW-M27C20 ... 3efab3fcca

OTP = One Time Programmable

In other words: They're PROMs, not EPROMs.

Which means, they cannot be erased.

ok, thanks. i thought they could be erased electronically or something

coinheaven wrote:ok, thanks. i thought they could be erased electronically or something

Those do exist though, EEPROMs.

Just thought I'd make it clear to the OP:

PROM = programmable ROM, otherwise known as OTP (one-time-programmable). You can write to it once and no more.

EPROM = erasable PROM. Has limited write cycles (think: limited number of times you can write to it). Erasing them requires use of a UV light and 1-2 hours of time. More expensive than PROM.

EEPROM = electronically-erasable PROM. Has limited write cycles like an EPROM. Erasing them can be done purely through software (usually the same software which does the writing). More expensive than EPROM.

FlashROM = flash-based EEPROM. Functionally the same as an EEPROM, with greater life expectancy (more write cycles). AFAIK is faster during writes/erasing. More expensive than non-flash EEPROM.

Hope this helps. To others more familiar with hardware stuffs -- if I got any of this wrong, please do correct me!

koitsu wrote:FlashROM = flash-based EEPROM. Functionally the same as an EEPROM, with greater life expectancy (more write cycles). AFAIK is faster during writes/erasing. More expensive than non-flash EEPROM.

Hope this helps. To others more familiar with hardware stuffs -- if I got any of this wrong, please do correct me!

FlashROM has fewer write cycles that EEPROM, and also is usually slower, but it's the most used because of its price: much less that any other rewritable solid state storage medium

The cheapest is the MaskROM, but it can be programmed only in big batches and is read-only

I don't think "PROM" and OTP EPROMs are the same thing. PROMs as I recall work by blowing fuses or anti-fuses to set bits. OTP EPROMs are just regular EPROMs but cheaper as they lack the quartz erasing window on the package. When you program bits (by setting them from 1 to 0) that's it. You can't go back. In theory if you could open the package and stick it in a UV Eraser that would work, but I'm not sure that is reasonably possible.

Use OTP chips only for things you know are final code/exactly what you want.

Anyone find smaller sizes for OTP chips like 27C32 and 27C128/256 for NROM boards? I've searched many times but can't find them that small and would like to get a few one day.

3gengames wrote:Anyone find smaller sizes for OTP chips like 27C32 and 27C128/256 for NROM boards? I've searched many times but can't find them that small and would like to get a few one day.

I don't see why you wouldn't want to get larger chips, as you can easily ground their higher address lines and "pretend" they are smaller chips. In fact, if small chips are indeed so rare, they might even be more expensive.

tokumaru wrote:

3gengames wrote:Anyone find smaller sizes for OTP chips like 27C32 and 27C128/256 for NROM boards? I've searched many times but can't find them that small and would like to get a few one day.

I don't see why you wouldn't want to get larger chips

How many pins do the larger chips have?

The small chips have 28 pins while the larger chips have 32 pins. In some cases, it's ideal to have the smaller chips because they are drop in replacements for some of the earlier boards.

Yeah. Like a 27C512 could be used for all of those 28-pin chips, that'd be fine. -goes off to find, hopefully I can this time-