Apple IIe - Page 254

254 Apple I le Users Handboo k
The computer cannot be made to do useful work unless it can be
given instructions. This is done by changing the contents of
memory.
To exte nd the metaphor a bit further, (since) the Apple lie is a
half-finished canvas, it can understand BASIC commands, store
copies
of programs on disk and perform numerous other input
and output functions . However, if one just randomly dabbed his
paint brush around the computer's memory, a nicely started
painting could be ruined.
There are a few places not to play around. The most important of
these is page-zero . Page-zero is where BASIC and DOS store
important variables about themselves. For example , the location
of the BASIC program is stored in page-zero. If page-zero must
be accessed (usually because of the 6502's indirect addressing
techniques), locations
F9 to FD can always be used safely.
Keeping this cautionary note in mind, here is how to change the
contents of memory. First, open the location to be changed.
*357
0357-FF
Now, type a colon followed by the new value you wish to store.
*:
47
*357
0357-47 - new value stored
These commands can be combined.
*357:86
*357
0357-86 - just to check
Just as there Was a shortcut for examining a large block of
memory , there is also a shortcut for changing large portions of
memory. To place the values 04 53 F88B FF in successive locations
starting at
3703 , enter the following:
*3703: 4 53 F8 8B FF
*3703
3703-04 -to check
*(ret) /
53 F8 88 FF