Commodore 64 Manual de usuario descargar pdf (Pagina 32)

ing register is set to 0, the first line is covered, ready for new data.

When the Y scrolling register is set to 7 the last row is covered.

For scrolling in the X direction, the scroll register is located in bits 2 to

o of the VIC-II control register at location 53270 ($DOI6 in HEX). As

always, it is important to affect only those bits. The following POKEdoes

this:

POKE 53270, (PEEK(53270)AND 248)+X

where X is the X position of the screen from 0 to 7.

For scrolling in the Y direction, the scroll register is located in bits 2 to

o of the VIC-II control register at location 53265 ($DOII in HEX). As

always, it is important to affect only those bits. The following POKEdoes

this:

POKE 53265, (PEEK(53265)AND 248)+Y

where Y is the Y position of the screen from 0 to 7.

To scroll text onto the screen from the bottom, you would step the

low-order 3 bits of location 53265 from 0-7, put more data on the

covered line at the bottom of the screen, and then repeat the process.

To scroll characters onto the screen from left to right, you would step the

low-order 3 bits of location 53270 from 0 to 7, print or POKE another

column of new data into column 0 of the screen, then repeat the pro-

cess.

If you step the scroll bits by -I, your text will move in the opposite

direction.

EXAMPLE:Text scrolling onto the bottom of the screen:

10 POKE53265,PEEK(53265)AND247

INTO 24 ROW MODE

2121PRINTCHR$(147)

CLEAR THE SCREEN

30 FORX=lT024:PRINTCHR$(17); :NEXT

THE CURSOR TO THE BOTTOM

40 POKE53265,(PEEK(53265)AND248)+7:PRINT

POSITION FOR 1ST SCROLL

5121 PRItHII HELLOII;

6121FORP=6T00STEP-1

70 POKE53265,(PEEK(53265>AND24S)+P

8121FORX=lT050:NEXT :REM

DELAo,.' LOOP

910 t~E:>o:T:GOT041O

:REM GO

:REM

:REM MOVE

:REr1

130 PROGRAMMING GRAPHICS

1 2 ... 27 28 29 30 31 32 33 34 35 36 37 ... 82 83

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