Commodore PET User Manual page 303

Sv replacing A with this equation. the PET will calculate the screen address itself.
POKE32768+(COL-)+(40*ROW-11.X
"- y----
POKE A
.X
For instance. if COL (C) and ROW (R) were input as 5.3. and X as
fi
then a
spade would be POKEd at screen location (3.5). address 32852.
10 INPUT
c.
R..
~y~
20 POKE 32768+(C-l)+(40*(R-l»,X
= 32768+(COL-1)+(40·(ROW-1)),X
= 32768+(5-1)+(40'(3-1)),X
= 32768+4+(40*21.X
= 32768+4+80.X
= 3285 .X
11 5
Although the above equation is useful when vou do not know the exact
screen address. vou should not alwavs incorporate that long equation into vour
programs. It is much neater and more concise if vou use the aforementioned for-
mula to calculate the screen address outside of the program. and then use the
screen address using POKE inside of the program:
POKE 32852,X
or
A=32852
POKE A,X
Variables are acceptable in the POKE commando as long as the variables stay
within the proper limits:
1. POKE 32768+A.X
2. POKE A,X
where A is a number between 0 and 999 inclusive
(32768+999=33767).
where A is a number between 32768 and 33767
inclusive.
POKE 32768 .. >:;
ft=ft+10
POKE :32768+ft,;"';
IF ft<=1000 GOTO 30
or:
1
(1
;;~0
30
40
Using variables to represent the screen address is practicable when POKE-
ing to a repeating sequence of screen spaces. For example. the two programs
below POKE the value of X ten spaces apart across the screen. This is a much
more efficient method of printing than programming several PRINT statements
and cursor movements.
1
(1
ft=32768
2(1
POKE A, X
:30 ft=ft+ 10
40 IF ft<=33767 GOTO 20
290