Section 2 - Commodore Computers

May, 1982, Issue 24 COMPUTEI 135
May. 1982, Issue 24 COMPUTE! 135
Did you ev,,' t)'pe NEW and "egret it? In theory, your
Did you ever type NEW and regret it? In theory, your
program in -memmy memory is i.s wil)ed wiped out by Iry the wm'd word NEW. On
the Atari, mem01) memory is, i.s, in, [acl" fact, washed clea.n dean with zeros,
zeros.
But the Apple AI)I)le a.nd and PETICBM com/mten computers just reset some
pointers (the program pmgralll is still in there). Here'sH how you
un-new,
un-new.
Recovering
Recovering
From NEW On
Apple And CBM
Apple And CBM
Jimmy Stephens
AthenS,GA
Jimmy Stephens
Athens, GA
If you are like me, at least once in your li fe you
If you are like me, at least once in your life you
have had that sickening feeling that comes with the
realization that you have just typed NEW, or maybe
realization that you have just typed NEW, or maybe
turned your computer off, without saving your
program. The next thing g you probably did was to
look for the nearest window tojump out. Unfortunately,
if you havejustlllrned turned off the computer, I
can't give you any alternative to jumping out the
can't give you any alternative to jumping out the
window. (Hopefully it's a text window.) What I can
do is to show you how to combat an accidental NEW.
When the NEW command is processed by
Apple and CBM computers, the program in memory
is not erased. All that happens is that several
pointers are reset so that, when the next program
pointers are reset so that, wh en the next program
is entered, it will write over the old one. If you
have entered NEW and have not written any lines
to a new program or loaded another program,
to a new program or loaded another program,
then your old program is still in memory and can
be recovered with a little work.
be recovered with a li llie work.
On both Apple and CBM, NEW destroys only
twO bytes of the actual program. Fortunately, these
two bytes of the actual program. Fortunately, these
two bytes deal with the length of the first line e of
the program and cann be recovered. The first POKE
to be made is POKE 2050,8 on the Apple or POKE
to be made is POK E 2050,8 o n the Apple or POK E
1026,4 on CBM. Now, try LiSTing the program.
1026,4 on CBM. Now, try LISTing the program.
Surprise! You shouldd see sec the first line of the program
on the screen.
Your next POKE will be determined by the
Your next POKE will be determined by the
number of bytes in this first line. Count the number
of characters in the line, remembering that reserved
BASIC commands are tokenized and take up onlyy
one byte. Therefore, count all BASICC commands
as one character. Add six to your total and POKE
as one character. Add six to your total and POKE
this value into location 2049 on the Apple or location
1025 on CBM.
There is a good chance, because of spaces in
the line and such, that this POKE will not be correct
the first time. LIST the program again. If it LISTs
the first time. LIST the program again. Ifit LISTs
O.K. then the POKE was right and you can skip to
the next paragraph. Otherwise, you will need to try
the next paragraph. Otherwise, you will need to try
a new value and redo the POKE. Keep trying values
around your original total until the program LISTs
around your original total until the program LISTs
correctl y.
correctly.
At this point, although it looks alright, do not
mn run the program. If you do, the variables will overwrite
the program and all your work will have been
for r nothing. Youu will have to make POKEs in a
pair of locations to reset the pointer for the be
pair of locations to reset the pointer fo r the beginning
of the variables. For CBM computers, these
locations depend on which ROM revision your
system has. For Original ROMs, these locations are
system has. For Original ROMs, these locations are
124 and 125, and, for both Upgrade and 4.0, ROMs
the locations are 42 and43. The Apple has a pointer
to the start of variable space as well as a pointer to
the end of the program. This means that if you
have an Apple, you will have to make all remaining
POKEs K in both of these locations. The first pointer
is at 105 and 106 and the second one resides at 175
and 176.
The next POKEs are designed to give your
program some room to breathe and are determined
by the amount of RAM you have. T hese POKEs
are onl y te mporary and will be changed later. Use
program some room to breathe and are determined
by the amount of RAM you have. These POKEs
are only temporary and will be changed later. Use
the formula below to determine the value of the
first POKE.
first POKE.
((Number of Kilobytes of RAM) * 4) -2
This POKE is made in the high byte of the
variabl e poin ter(s). Next, POKE 0 into the low byte
variable pointer(s). Next, POKE 0 into the low byte
of the pointer(s). For example: On a 16KK Apple,
the operation would look like this
the operation would look like this
POKE 105,0: : POKE 106,62: : POKE 175,0:
:
POKE 176,62
POKE 176,62
Your program will now run, but, if it uses
lots of variables, you will soon get an OUT OF
lots of variables, you will soon get an OUT OF
MEMORY message. Too fix this, add the following
lines to your program:
o 0I=XXXX
1I 1=1+ I = I+1:IFPEEK(I)81THEN1
I:IFPEEK(I) 8ITHENI
2 IFPEEK(I+1)81THEN1
+ 8ITHENI
3 1= I = I 1 + 6:A = INT(I/256):B = 1-256*A
I-256*A
4 POKEYY,B:POKEZZ,A:END
63999 QQ
XXXX = 1024 for CBM or 2048 for Apple.
XXXX = 1024 for CBM or 2048 for Apple.
YY::::: = low byte of variable pointer(s).
ZZ::::: = high byte of variable pointer(s). (Two more POKEs
for the second pointer will be necessary on the Apple.
for the second pointer will be necessary on the Apple.
When the program is run, it will change the
POKEs to the correct value. Obviously, if your
program's first line number is less than five orr if it
has a line numbered 63999, you wi ll have to make
has a line numbered 63999, you will have to make
some adjustments. Also, you will need to make
sure that "QQ" does not appear anywhere else in
the program. IfI f it does, you will have to useu ~e another
two-letter sequence in line 63999 and you will \yill need
to adjust the ASCIII codes in lines one and two
accordingly. ©
accord in gly. ©