1541 ROMs

I have compared all the 1541 ROMs. The results are below. I have list the 
-02 and -06 ROMs as revisons 1a and 2a because the are almost identical to 
revisons 1 and 2, and because Commodore didn't think they were significant 
enough to release world wide.


         ROMs          Revision
325302-01, 901229-01     r0
325302-01, 901229-02     r1a Japan
325302-01, 901229-03     r1
325302-01, 901229-05     r2
325302-01, 901229-06     r2a Europe
      251968-01           r3  1541B/C
      251968-03           r4  1541-II

      Number of differences between ROMs

901229-02 |  14
901229-03 |  16    3
901229-05 |  93   86   84
901229-06 | 102   95   93   10
251968-01 | 179  172  170   87   78
            ------------------------
901229-      01   02   03   05   06

901229-02 and previous versions use a header gap of 8 bytes. 901229-03 and
later versions use a header gap of 9 bytes. This is the only difference
between 901229-02 and 901229-03.

901229-04 is unknown. 901229-05 changes some of the serial bus routines,
and NOPs out the auto start routine. 901229-04 could potentially make only
some of these changes, if it exists.

901229-06 adds a patch that sets location $51 (current track) to $FF before
formatting a disk. This is apparently to recover from a prior failed format
attempt. This is the only difference between 901229-05 and 901229-06.

901229-07 is known only from the parts list of the 1541B/C. It is probably
the same as the upper half of 251968-01.

251968-03 is substantially different, even in the $C000-DFFF region.

wlevak@sdf.lonestar.org
SDF Public Access UNIX System - http://sdf.lonestar.org

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