Commodore 64 Manual do Utilizador descarregar pdf (Página 11)

2) Your character set takes memory space away from your BASIC

program. Of course, with 38K available for a BASIC program,

most applications won't have problems.

WARNING: You must be careful to protect the character set from being overwritten

by your BASIC program, which also uses the RAM.

There are two locations in the Commodore 64 to start your character

set that should NOT be used with BASIC: location 0 and location

2048. The first should not be used because the system stores important

data on page O. The second can't be used because that is where your

BASIC program starts! However, there are 6 other starting positions for

your custom character set.

The best place to put your character set for use with BASIC while

experimenting is beginning at 12288 ($3000 in HEX). This is done by

POKEing the low 4 bits of location 53272 with 12. Trythe POKE now, like

this:

POKE 53272,(PEEK(53272)AND240)+ 12

Immediately, all the letters on the screen turn to garbage, This is

because there are no characters set up at location 12288 right now. . .

only random bytes. Set the Commodore 64 back to normal by hitting

the .:mlr~'111111key and "then the .~j:l-'1(oI~j:llkey.

Now let's begin creating graphics characters. To protect your char-

acter set from BASIC, you should reduce the amount of memory BASIC

thinks it has. The amount of memory in your computer stays the

same. . . it's just that you've told BASIC not to use some of it. Type:

PRINT FRE(O)-(SGN(FRE(O»<O)*65535

The number displayed is the amount of memory space left unused. Now

type the following:

POKE 52,48:POKE56,48:CLR

Now type:

PRINT FRE(O)-(SGN(FRE(O»<0)*65535

PROGRAMMINGGRAPHICS 109

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Commodore 64 Manual do Utilizador Página 11