Your Commodore - Commodore Is Awesome

computer think that you have typed
LOAD FILE,8,1 so it will go off to the
disk drive and LOAD the program
called file. There is one carriage return
left in the keyboard buffer. The cursor
is now over the keyword RUN and
when the RETURN is executed the
computer thinks you have typed RUN.
Simple isn't it?
If you are confused read the
explanation again and play around
with the program in FIGURE 2.
Quite often you will come across a
program which when the loader for it
is RUN, proceeds to POKE itself into
the same memory locations as the
loader program. This of course will not
work. In order to overcome this
problem you have to move the start of
Basic so that the Loader program and
the machine code will be at two
different memory locations. Memory
locations 43 and 44 (45 and 46 on the
CI 28) hold the start of Basic. Location
43 holds the low byte off the address
and location 44 holds the high byte.
The following formulae can be used to
work out the numbers to be POKED
into the relevant memory locations:
LOW BYTE = ADDRESS - 256* INT
(ADDRESS/256)
HIGH BYTE = INT (ADDRESS/
256)
Where address is the memory location
where you want Basic to start
One further point worth raising is
that the memory location before the
start of Basic should always contain a
zero. For example if you had moved
Basic to memory location 2000,
location 1999 should be POK Ed with a
zero. Commodore 128 owners have an
advantage over C64 owners when it
comes to SAVEing a prograrn, they
have a machine code SAVE instruction
in Basic 7.0 as well as the one in
the monitor. C64 owners have to resort
to POKEing into memory yet again.
We have already said that locations
43 and 44 hold the start of Bask.
Memory locations 45 and 46(47 and 48
on the CI 28) hold the memory address
of' the end of Basic. Whenever a SAVE
is performed the computer looks at
these memory loca-tions to see what
area of memory it should SAVE to
whatever device you are using. If you
POKE these memory locations with
the start address and end address of
your machine code program you will
be able to SAVE your code. The
C64 AND C12811
memory locations should be POKEd
with the following values:
43 low byte of start address
44 high byte of start address
45 low byte of end address
46 high byte of end address
The formulae already given can be
used to work out the numbers to be
POKE&
Of course, since you have moved
Basic, you will not be able to list any
programs in Basic memory until you
reset the memory locations to their
original values.
One more problem that you may
come across is the fact that the
machine code program to be turned
into DATA statements sits at the same
memory location as the Data Maker
Data Maker C64
PROGRAM: DATAMAKER-C64
Please read 'LISTINGS'
before entering program.
10 10 81,-145 :LN-70 :SA-4915
2
F9 20 FOR L-0 TO BL:CX-0:FOR D-
O TO 15
9F 30 READ A:IF A>255THENPRINT"
NUMBER TO LARGE":1.N*(1,*10S
TOP
28 40 CX-CX-PA:POKE
NEXT D
A9 50 READ AilF A>