Commodore 64 Uživatelský manuál stáhnout pdf (Strana 28)

The bit of that byte is:

BIT

= 7-(X AND 7)

Now we put these formulas together. The byte in which character

memory dot (X,Y) is located is calculated by:

BYTE = BASE+ ROW*320+ CHAR*8+ LINE

To turn on any bit on the grid with coordinates (X,V), use this line:

POKE BYTE, P.EEK(BYTE) OR 2jBIT

Let's add these calculations to the program. In the following example,

the COMMODORE 64 will plot a sine curve:

5121 FOR:X:=0T0319STEP. 5: REr1 WAVE WILL FILL THE SCREE~I

60 Y=INTC9121+80:f.SINCX/1121»

7(1 CH= I tH C;";/8::-

8121 RO=INTC'T'/8::-

85 UI='r'AND7

90 B'T'=BASE +RO*32121+8*CH+L~1

1121121BI=7-C:X:AND7)

11121 POKEB'r'" PEEK CB'r' ::0OR 0:2 t:E: I ::-

12121 t'IE:":n~

125 POKE1024..16

13121 GOT0130

The calculation in line 60 will change the values for the sine function

from a range of + 1 to -1 to a range of 10 to 170. Lines 70 to 100

calculate the character, row, byte, and bit being affected, using the

formulae as shown above. Line 125 signals the program is finished by

changing the color of the top left corner of the screen. Line 130 freezes

the program by putting it into an infinite loop. When you have finished

looking at the display, just hold down .:m/'~"tI'I:Iand hit .'1:1.'11I1'1:11.

126 PROGRAMMING GRAPHICS

1 2 ... 23 24 25 26 27 28 29 30 31 32 33 ... 82 83

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Commodore 64 Uživatelský manuál Strana 28