Using EPROM's of a larger KB size


In some cases, not all, a larger KB sized EPROM can be used directly (i.e. no adapter) in place of a smaller KB one.

It usually comes down to the pinout of the EPROM's concerned.  Sometimes the pinout is different enough that an adapter would need to be used.

Whether an adapter is required or not, there is something else to be considered.  For example, if my clone motherboard is designed for a 27C128 EPROM (i.e. 16 KB sized), and I use a 27C256 EPROM (i.e. 32 KB sized), my motherboard does not see all of the 32 KB; it only sees one of the two 16 KB sized blocks within the 27C256.  In the example just given, because the 27C256's A14 pin will always be HIGH, my clone motherboard will only see the second of the two 16 KB sized blocks within the 27C256.

Going forward with that particular example, when I go to program the 27C256, I have two options:
- Program the 16 KB sized code/data file into the second half of the 27C256; or
- Double the 16 KB sized code/data file to create a 32 KB sized file, and program the 32 KB sized code/data file into the 27C256.

Most people choose the latter.  In that way, because all of the blocks are the same, you don't need to do an investigation as to which block is going to be seen by the motherboard.


Doubling, tripling, quadrupling, etc.


Option #1 - The COPY command of DOS

In this example, I have an 8 KB sized code/data file named SOURCE.BIN, which I need to quadruple (x4) for a 32 KB sized EPROM.
The command below will quadruple SOURCE.BIN file, creating the 32 KB sized TARGET.BIN file.

C:\>COPY SOURCE.BIN /B + SOURCE.BIN /B + SOURCE.BIN /B + SOURCE.BIN /B TARGET.BIN /B


Option #2 - Use of ROMFILL.EXE

An alternate to COPY, is the DOS tool named ROMFILL.EXE at here.
For example, if I want to quadruple the 8 KB sized file named TEST.BIN to produce a 32 KB sized file named TARGET.BIN, I use the following command.

C:\>romfill /32 test.bin target.bin