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the ATMEL AT29C256 chip is the de facto FLASH-ROM chip in use. It uses a 5V programming voltage, can be erased repeatedly electronically. They can be reused many times (about 100,000) without "wearing out." It is not significantly more expensive than OTP ROMs, and can save a lot of time compared to UV-Erase chips when many program changes are needed. This is because EPROMs must be erased in a special ultraviolet eraser device which takes 15-30 minutes, which is another advantage of the flash chips - you don't need a UV eraser! These flash chips are pin-compatible with 27 C256 chips. Some people have difficulty with the Atmel chips. Another recommended part is SST's 27SF256 it is also a flash chip (most 27-series chips are UV-Erase only)


on page 14 of the AMD29C256 Datasheet, directly after the base part number, the 2 digits are the speed of the ROM (90ns; 70, 120 (12) and 150 (15) are also available).

Then the first letter:

  • "J" is PLCC package (square 32-pin package)
  • "P" is DIP (this is what you want, unless you're doing your own thing)
  • "T" is TSOP

The second letter - operating temp range code:

  • "C" means commercial and is rated for 0-70C (32F to 158F)
  • "I" means industrial and is rated for -40 to 85C (-40F to 185F) If you have a choice, get this one, because it can get very, hot inside your car in the summer.

Note: most OBD0 PR3 and PW0 ECUs I've seen are very picky about these chips, and frequently throw random solid CELs when using them - all speeds, including 90ns. I would advise using other chips in these ECUs.

Revision: r1.1 - 25 Nov 2004 - 12:45 GMT - ltdannear { Edit | Attach | History | More }
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