When
vou press additional keys
while
the A
is
being displayed. the addi-
tional characters are stored in the keyboard buffer beginning at the next available
location. Suppose vou type in A and
while
A
is
being displayed vou type in
B.
C.
D.
and
E.
These characters are ail stored in the keyboard buffer:
Keyboard
Buffer
A
2
B
3 C
4
D
5
E
6
7
8
9
10
If
Vou
let the program continue, it
will
successively display ail the letters
stored
in
the keyboard buffer.
After
A
is
finished. the program fetches
Band
dis-
plays
it
across the 20 lines. then it fetches C and displays
it
etc.
What
happens if vou type in more than ten characters?
At
the tenth
character the buffer pointer wraps around, and continues storing the characters
being keyed in from position 1 of the buffer. If vou type in the first eleven letters of
the
alphabet
A-K. the first ten letters are stored in the ten buffer locations. then
the letter K
is
stored back in the first buffer location. overlaying the A:
Keyboard
Buffer
2
3
4
5
6
7
8
9
10
K
~
B
C
D
E
F
G
H
1
J
K overlays the A
When
the program finishes displaying the
A,
it
returns
to
fetch another
character.
But
the
PET
has
already fetched the character in location
1,
so
it
con-
siders the buffer empty! Keying in exactly eleven characters, or multiples of
775
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