Commodore Plus 4 - Page 334

322 Machine Language on the Commodore Plus/4
POKE 55, low byte of new top of RAM plus one
POKE 56,high byte of new top of RAM plus one
CLR
To execute machine code that is located underneath the BASIC or operating
system ROM, the routine must begin somewhere NOT underneath the ROMs
and bank in RAM (see the section on banking) before transferring control. The
transfer code could be located in the cassette buffer ($0333-$03F2) or some other
safe location. The machine code routine must bank ROM in before returning to
BASIC. The pointer to the top of memory at 1331-1332 ($0533-$0534) must also
be changed in some applications.
Moving the bottom of BASIC up can be accomplished with the following:
POKE 43, low byte of new bottom of RAM
POKE 44,i2igZ2 byte of new bottom of RAM
POKE pew bottom of RAM minus one,0
NEW
Note: The pointer to the bottom of memory at 1329-1330 ($0531 -$0532) does
not appear to be used by BASIC.
After executing these commands, machine code could be placed in the vacated
RAM at $1000. The GRAPHIC command moves the bottom of BASIC up $3000
from its location before the command is given, and GRAPHICCLR moves it
down $3000 back to its original location. But the graphic screen itself is always in
the same position at $1800-$3FFF. Care must be taken to avoid conflicts.