May June 1980 - Commodore Computers

48 COMPUTE. MAY/JUNE. 198O 1980 ISSUE 4a
Using The PET's Second CasseHe
Using The PET's Second Cassette
Buffer To Increase Available
Memory Space
Chuck Stuart, President
CMS Software Systems, Inc.
5115 Menefee Drive, Dallas, TX 75227
If you have tried all the known memory savingg
tricks to reduce the size of your new super program to
save mankind and it still won't t fit into your PET's
available able memory, you might be able to save the day
by storing part pan of the program in the PET's second
cassette buffer.
The second cassette buffer begins at address 826
and extends through address 1023. If your program
does not use the second casselte cassette then you call can use
thiss 197 bytes for r program storage. Granted, 197
bytes may not see m like a lot of extra space, but
bytes may not seem like a lot of extra space, but
used correctlyy it can save you several limes times that
much space in the PET's regular memory.
.
Suppose, forr instance, your program requires res a
deck of 52 cards to be stored in memory. . Such a deck
wou ld normally contain the va lues 1 through 52 a nd
would normally contain the values 1 through 52 and
be stored in an integer array referenced by a name
like D % . Si nce each clement in an integer array re­
like D%. Since each element in an integer array re
quires two bytes of memory and there are 52 elements
in QU ourI' array, we can sec see that, al, s[O stored rc ci as a normal
integer r array, our cleck deck of cards would require 104
bytes of storage space plus atl least another 7 bytes
and probably more to properly di mension the array.
and probably more to properly dimension the array.
Since no array clement element value exceeds 255, this
array could easily be stored in the second cassette
buffer with each element requiring only one byte fo r
buffer with each element requiring only one byte for
slOrage storage. . By moving g our deck of cards inlO into the
second cassette buffer we have saved a minimum
of 111 bytes of main memory while e using only 52
bytes of the 197 available able to us in the second cassette
buffer. T hi s same method works equally well for single
buffer. This same method works equally well for single
clement integer variables and strings.
If you simply usc use this extra space for temporary
storage of information during program operation then
no special problems are crea ted. If yo u make full
no special problems are created. If you make full
usc use off the second cassette buffer for permanent
storage of program data such as operator prompts,
suit symbols for your card deck, orr other values
normally stored in DATA Slalements, statements, etc., then the
second cassette bu ffer must be stored along with the
second cassette buffer must be stored along with the
main program. Since the SAVE command begins
s
savingg att locationn 1024, any data stored below that
address in the second cassette buffer would not be
saved by using the standard SAVE command.
Fortunately by us ing the PET's built-in ROM
Fortunately by using the PET's built-in ROM
Monitor o r wee can specify the exact beginning and ending
addresses we want to save. If you still have the
old ROM set without a Monitor don'tt panic. I I'll ' show you how to save the buffe r a li ttle later.
show you how to save the buffer a little later.
The first thing you have to do is determine thee
address range you want to save in hexidedmal. idecimal. As
we pointed Out out bcfore, before, the second cassette buffer
begins al location 826 decimal or 033A in hex so we
begins at location 826 decimal or 033A in hex so we
know that we want to start saving at location
033 A hex . To determine the ending address yo u must
033A hex. To determine the ending address you must
first save your program onto tape using g the normal
SAVE command, and then load it back into memory
with the LOAD command. . Data stored in the second
cassette buffer will not be affected by this operation.
Now type PRI NT PE EK( 43)'256 + PEEK(42). The
Now type PRINT PEEK(43)*256 + PEEK(42). The
answer you get willw be thc the address in decimal where
your program ends and which you must now convert
to hex. (If you've never taken the e time to LO learn how
to 1O convert decimal to hex and vice versa because
you figured you wouldd never need to know then you
were wrong.)
Now that you know the memory range you want
to save, enter the Monitor by typing SYS1024 aand
pressin g RETURN. To save your program including
pressing RETURN. To save your program including
the data slO stored in the second cassette buffer, type
the following g line exactly, substitutingg the eending
address for XXXX and filling ing in your own program
name, and press RETURN:
S ""PROGRAM NAME",01,033A,XXXX
NAME",OI ,033A,XXXX
PET will di splay the slandard PRESS PLA Y AND
PET will display the standard PRESS PLAY AND
RECORD message aand then save your program onn
tape in the normal manner except it will begin
saving at location n 826 instead of the usual
location 1024 where you r BASIC program begin s.
location 1024 where your BASIC program begins.
You can LOAD aand use usc thee program ra m in the normal
manner except that you must always use the Monitor
to save the program or else you will lose any data
slOred stored in the second cassette buffer. This means that
no one else will be able to copy you r program un less
no one else will be able to copy your program unless
they know the secret. There is one other thing to
remember. If you make any changes to your program ,
remember. If you make any changes to your program,
don't forget 1O to redetermine the new ending address
before using the Monitor to resave the e program.
If you have the old ROM set wilhoul a Monitor
If you have the old ROM set without a Monitor
then you can accomplish the same result resuh in the
followingg manner:
A) Save the program with the SAVE command
and then reload it with the LOAD command.
B) Type POKE247,58:POKE248,3 POKE248,3 and press
RETURN.
C) Type SYS63153 and press RETURN.
PET will display the standard PRESS PLAY AND
RECORD message and save the progra m beginn in g
RECORD message and save the program beginning