* 2732 / 2732A / 27C32 EPROMs

The stock EPROMs used in these ECMs could be any variety of 2732 (i.e. 2732, 2732A or 27C32). Since GM generally only marked the EPROMs with their proprietary part numbers its difficult to determine which type of EPROM was used. It doesn't matter which of these EPROM types you select in the EPROM programmer software when you read the EPROM so you can select a 2732 type EPROM and read any of them. However, when you program the EPROM, you must select the correct EPROM type. If you use the wrong type during programming you'll very likely damage the EPROM. For this reason, we recommend that you not erase and reprogram the original EPROM but purchase a replacement EPROM of a known type.

** 27C128 EPROMs

27C128 EPROMs were never very popular and they can now be difficult to find. A 27C256 EPROM which is much more common can be used in place of a 27C128 but when you program a 27C256 EPROM with a calibration file from a 27C128 you need to program the upper half of the 27C256 EPROM with the calibration file. To do this select 27C256 as the EPROM type in the EPROM programmer software and then set the starting address at 4000 hex. Then load the calibration file and program the EPROM.

Similarly, when you read a 27C256 that has been used to replace a 27C128 EPROM you should only read the upper half of the EPROM by setting the starting address to 4000 hex before reading the EPROM.