Commodore 128 Programmer's Reference Manual page 260

250 COMMODORE 128
0
Now you are ready to enter C64 mode and run the program with the following ^
command:
GO 64 LJ
Reply to the question "ARE YOU SURE?" by pressing the "Y" key and
RETURN. You are now placed in C64 mode. j j
At this point, you may say to yourself, "After I just did all that work, why am I !J
going to waste it by changing modes?"
Actually, you are not wasting any effort. When you GO 64 (or press the reset , ,
button), much of the RAM for machine language programs and data is preserved in jj
RAM bank 0. BASIC programs are erased, however. Specifically, these are the ranges
of RAM that are preserved when changing between C128 and C64 modes:
__ u
C128 MEMORY LAYOUT - .
$0C00 - $0DFF RS232 Input and Output Buffers ]J
$1300 - $1BFF Available Memory for Machine Language application programs
$1COO - $1FFF Bit Map Video Matrix
$2000-$3FFF Bit Map Data 1 j
$4000 - $FF00 BASIC Text Area U
Figure 8-27. Preserved RAM Between CI28 and C64 Modes
The rest of the RAM memory is allocated for other purposes and the contents
change from mode to mode. There are other particular bytes that are preserved from I j
mode to mode, but these small chunks of memory are not worth mentioning here. The °
blocks of memory mentioned above provide enough of a clue to the RAM used by both
modes. Remember, however, that the RAM is only preserved if you switch from C128 j
mode to C64 mode with the GO 64 command, or you switch from C64 to C128 mode ^
with the reset button (warm start). If you perform a cold start, turn the computer power
off, then on again, all RAM is cleared and none is preserved. \ j
Notice that the address ranges where you placed your program, the video LJ
matrix and the bit map are in the portions of RAM that are preserved from mode to
mode. /
f
O
Now start (run) the program from C64 BASIC with this command:
SYS 12*256
The top three quarters of the screen is the bit map screen you created with the
C128 BASIC graphics commands, the lower quarter is horizontally scrolling text. \ I
The following program is the listing that performs the split screen and scrolling. Li