Chapter 11 - The character set
The letters, digits, punctuation marks & so on that can appear in strings are called characters
, & they make
up the alphabet, or character set, that the ZX81 uses. Most of these characters are single symbols, but
there are sone more, called tokens, that represent whole words, such as
PRINT
,
STOP
,
**
, & so on.
There are 256 characters altogether, & each one has a code between 0 & 255. There is a complete list
of them in appendix A. To convert between codes & characters, there are two functions,
CODE
&
CHR$
.
CODE
is applied to a string, & gives the code of the first character in the string (or 0 if the string is empty).
CHR$
is applied to a number, & gives the single character string whose code is that number.
This program prints out the entire character set.
10
LET
A=0
20
PRINT
CHR$
A;
30
LET
A=A+1
40
IF
A<256
THEN GOTO
20
At the top you can see the symbols ", £, $ and so on up to Z, which all appear on the keyboard & can be
typed in when you have the cursor. Further on, you can see the same characters, but in white on black
(inverse video); these are also obtainable from the keyboard. If you press
GRAPHICS
(shifted 9) then the
cursor will come up as : this means graphics mode
. If you type in a symbol it will appear in its inverse
video form, & this will go on until you press
GRAPHICS
again or
NEWLINE
.
RUBOUT
will have its usual
meaning. Be careful not to lose the cursor amongst all the inverse video characters you've just typed in.
When you've experimented a bit, you should still have the character set at the top; if not, then run the
program again. Right at the beginning are space & ten patterns of black, white & grey blobs; further on
there are eleven more. These are called the graphics symbols
& are used for drawing pictures. You can
enter these from the keyboard, using graphics mode (except for space, which is an ordinary symbol using
the cursor; the black square is inverse space). You use the 20 keys that have graphics symbols written
on them. For instance, suppose you want the symbol , which is on the T key. Press
GRAPHICS
to get
the cursor, & then press shifted T. From the previous description of the graphics mode, you would
expect to get an inverse video symbol; but shifted T is normally
<>
, a token, & tokens have no inverses: so
you get the graphics symbol instead.
Here are the 22 graphics symbols.
To Next Page
Loading...
Need help?
General
