I really only need to do about 6 of these.

I was doing some searching and found I can get replacement eproms for under $4 each, at that price I don't think a purpose built eraser is warranted. Where in the World are you, it helps to know so we can advise on suppliers. Although they do degrade each time they are reprogrammed, you should get about 500 cycles per IC which in most cases equates to centuries of use! You can reuse the same IC many times over. I advise you to get a purpose made EPROM eraser rather than try to make one yourself. Erasure is usually complete in 20 to 25 minutes with the IC around 25mm (1') away from the tube. The tube will normally use mercury vapor and emit light at around 245nM which is extremely dangerous to look at or expose skin to for more than a few seconds, hence the light proof box. There are special erasers which are safe to use, they have a drawer in which the IC is placed which slides inside a light proof box under the UV tube. Don't worry about removing the labels for a brief period, even in bright sunlight they took days to erase so a few moments in room light is quite safe. To erase the ICs you need a UV light source. The only danger is using slower access time devices which *may* not work but probably will. The access time is important but any device with 120nS or faster access will work OK. Most, if not all, later devices used 12.75V and modern day replacements will almost certainly use that voltage.

The 27C256B 12F1 uses 12.75V programming voltage and has 120nS access time. It was quite normal for non 'C' to be replaced by 'C' to make the circuit more power efficient. The 'C' version uses CMOS technology which had much lower power consumption but was otherwise almost identical. The 27256 and 27C256 are essentially the same device, in the early days they used a slightly different technology, PMOS and NMOS. Once I retrieve the data from the eprom, can I then erase the old one's and put the new program on them? I know these need light to be erased, but what kind of light? How much? etc.etc. Also, you mentioned that some chips want certain voltages, how do I know if the burner is capable of both the voltages that will possibly be needed?ģ. Is there a cheap burner that will let me read and write both of these if need be? I assume if it'll do one it should do the other and all the varients?.but I want to be sure before I buy something that doesn't work!Ģ. Ok.so, here's a few more questions then.ġ. Hmm.I just peeled back some of the older chip and found this next to the 'ST' manufacturer symbol.Īpparently they used different chips in the past.I assume its an older variant of the m27c256b. That is on the newer chip that they sent me. Ok.they have stickers over the windows and part numbers, and I don't want to remove them until I'm able to read them! I have peeled one side back enough to see this though.

27c256 eprom programmer