i just found a motherlode of 2764's in a heap of old computers. can they be interchanged with 27C64's? if not then what differences should i know about?
the middle letter specifies the technology used to make the device. IF they have a clear window (under a sticker, maybe), then you can erase them and reprogram them.
Note, however, that a 2764 is only 64kilobit, or 8kilobyte: It would take 3 or 5 to support the tiniest of NES games. They would be far more practical for making Atari 2600 repros.
The "C" means that they are CMOS devices, devices without the "C" are old style NMOS devices. The important differences here are the speed and the power consumption. CMOS devices draw less power and tend to be faster. I've noticed that when using non-CMOS EPROMs in NES games, they tend to get kinda warm.
Also, as lidnariq pointed out, 2764's are only 8k, so aren't a whole lot of use for NES games - but I use them all the time in Atari 2600 carts though.
-Ian
lidnariq wrote:
Note, however, that a 2764 is only 64kilobit, or 8kilobyte: It would take 3 or 5 to support the tiniest of NES games. They would be far more practical for making Atari 2600 repros.
Or NROM CHR ROMs, if you can dumpster-dive a bunch of 27C128 or 27C256 parts to use for the PRG.
tepples wrote:
lidnariq wrote:
Note, however, that a 2764 is only 64kilobit, or 8kilobyte: It would take 3 or 5 to support the tiniest of NES games. They would be far more practical for making Atari 2600 repros.
Or NROM CHR ROMs, if you can dumpster-dive a bunch of 27C128 or 27C256 parts to use for the PRG.
thanks, Tepples. you always seem to have the straight answer that I'm looking for. they're PERFECT for an 8KB CHR bank, as long as they're the right size and pinout...does the different response time mean i might get graphical glitches?
also, is it possible to use a 8KB or smaller ROM as a PRG? iirc, all that's necessary is to tie certain address pins high or low, ok i forget.
pps...power consumption... not a problem on the NES, right?
Roni wrote:
also, is it possible to use a 8KB or smaller ROM as a PRG? iirc, all that's necessary is to tie certain address pins high or low, ok i forget.
You can, but there are no commercial games that will fit -- the smallest is 16kB. You'll need to use two and some external logic. Address lines generally do not need to be tied high or low if the ROM is smaller than the space you're mapping it into.
lidnariq wrote:
Roni wrote:
also, is it possible to use a 8KB or smaller ROM as a PRG? iirc, all that's necessary is to tie certain address pins high or low, ok i forget.
You can, but there are no commercial games that will fit -- the smallest is 16kB. You'll need to use two and some external logic. Address lines generally do not need to be tied high or low if the ROM is smaller than the space you're mapping it into.
ok but i'm not planning to reproduce commercial games, this is for demos and test ROMs only (artROMs too)
Yeah, you can fit a decent amount of stuff in 8kB. Not a lot, but hey. Bigger roms are only like $1, so it's not a huge money saver really. Unless your program really doesn't need to be bigger. (and you can't really buy 8kB EPROMs anymore, not cheap new ones anyways).
IIRC, the game Galaxian used 8kB for both PRG and CHR.
it's all good, my options are constantly expanding as long as people keep throwing out 386's. I just scavenged two 27C256's from a video card and a 27C512 from a keyboard adapter on a motherboard whose service tag read 1992.
RetroHacker wrote:
The "C" means that they are CMOS devices, devices without the "C" are old style NMOS devices. The important differences here are the speed and the power consumption. CMOS devices draw less power and tend to be faster. I've noticed that when using non-CMOS EPROMs in NES games, they tend to get kinda warm.
Also, as lidnariq pointed out, 2764's are only 8k, so aren't a whole lot of use for NES games - but I use them all the time in Atari 2600 carts though.
-Ian
Thank you, RetroHacker, for that important detail. Definitely essential information.
Which reminds me also, it'd be worth looking up your burner's support for the chips, because I seem to remember seeing older NMOS EPROMs requiring some different programming voltages. I'm not sure if that was only chips before the 2764 though. It should list 2764 and 27C64 seperately.
Quote:
Which reminds me also, it'd be worth looking up your burner's support for the chips, because I seem to remember seeing older NMOS EPROMs requiring some different programming voltages. I'm not sure if that was only chips before the 2764 though. It should list 2764 and 27C64 seperately.
Yes, your programmer needs to know exactly what chip is in it for best results. The programming voltage is different between some of the older chips. There exists both 2764 and 2764A chips - both not CMOS, but both have different progamming voltage requirements. Same story with 2732 and 2732A's.
IIRC, the voltages are the same for the "A" parts and the "C" parts in most cases, but still, it's best to select the correct part...
-Ian
the specs for the programmer i ordered says it supports 12V power mode so i guess as long as i have the correct input power supply it should work, right?
http://cgi.ebay.ca/ws/eBayISAPI.dll?ViewItem&ssPageName=STRK:MEWNX:IT&item=130279341492