pattern generator utility (PFILL) from the Welcome software and which is

described at the end of this chapter. Further information about the way the

VDU23 command works is given in the Reference Manual.

PFILL lets you define your own pattern and displays the numbers needed to

recreate it. The numbers are shown in hexadecimal form (counting in 16s). Do

not worry if you are not familiar with hexadecimal. You need only put these

numbers in a suitable VDU statement to use the pattern in your own

programs. For example:

122 VDU23,2,&A0,&50,&A0,&50,&A0,&50,&A0,&50

is the hexadecimal equivalent of the previous line 122 and has the same effect.

(The & symbol is used to denote that the number following is in hexadecimal

notation. )

Defining your own characters

VDU 23 can also be used to define new characters for games or for specialist

programs in science or mathematics which require unusual notation. You may

recall that the symbol for pi was used as an example in the introduction to this

guide.

AI] the normal characters are based on an 8 by 8 grid, so the upper-case A looks

like this:

Any of the characters can be redefined, but changing the upper-case A to some

other shape does not help the readability of programs!

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