I have made another version of 64GS EPROM. This one restores the Basic
warm start vector to it's usual value. This version now comes up in
Basic, just like any C64. The GAMES System screen can be accessed by
SYS63278. With this version I can examine the system easier.
Summary of changes in the 64GS ROM:
E449-E448 The Basic warm start vector has been changed from $A483 to
$F72E. (This is the vector I changed)
JSR's to various tape routines have all been changed to
JSR $FB4D
All the tape routines have been removed, even though this frees
up more space than is needed for the games screen.
F72C Alternate entry point for the games screen. The background
colors are set and then returns.
F72E-FB4C Main entry point for the games screen. The screen is printed
and goes into a loop moving the graphics. The graphics data is
in the last part of this section.
FB4D JMP F707 Redirected tape routines jump to error message. This
is an unnecessary step as they could have jumped directly to
the error routine.
00 fill bytes where the remaining tape routines were.
FC00 FC3F Copyright notice.
FD83-FD85 The power up memory test routine is modified to test only one
byte in each page. This greatly reduces the duration of the
blank screen on power up.
FD9B-FDA2 Tape routine interrupt vectors have been redirected to the end
of the NMI interrupt routine.
It seems strange that so much care was taken to clean out the tape
routines if it was not intended that Basic should be used. But, pressing
the "LOAD" key gives an error, instead of being redirected to device 8 as
in the SX64.
Modifying the ROM is not the ideal way to get into Basic. It should be
possible to make a game cartridge that restores the Basic warm start
vector and then exits back to Basic. This may be what Commodore intended,
but that would require a keyboard.
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