1 REM PAGE FLIPPING EXAMPLE
2 REM BY JASON H. MOORE, PH.D.

10 REM *** INITIALIZATIONS ***
20 POKE 106,PEEK(106)-4
30 GRAPHICS 2+16
40 SETCOLOR 0,0,14:SETCOLOR 4,7,0
50 PRINT #6;"LOADING SCREEN DATA"
60 DL=1536:DLHI=6:DLLO=0
70 DIM VBI$(10)
80 POKE 203,30:REM Vertical blank counter for delay
90 POKE 204,0:REM Page counter to keep track of flips

100 REM *** SETUP SCREEN MEMORY ABOVE RAMTOP ***
110 SCRLO=0:SCRHI=PEEK(106):SCR=SCRHI*256+SCRLO
120 POKE 205,SCRHI:REM Store high byte in memory 205
130 FOR I=0 TO 239
140    POKE SCR+I,17:REM     SCREEN 1 (1s)
150    POKE SCR+256+I,18:REM SCREEN 2 (2s)
160    POKE SCR+512+I,19:REM SCREEN 3 (3s)
170    POKE SCR+768+I,20:REM SCREEN 4 (4s)
180 NEXT I

200 REM *** SETUP DISPLAY LIST ON PAGE 6 OF MEMORY ***
210 REM *** WITH LMS FOR FIRST PAGE OF SCREEN DATA ***
220 POKE DL+0,112
230 POKE DL+1,112
240 POKE DL+2,112
250 POKE DL+3,7+64:POKE DL+4,SCRLO:POKE DL+5,SCRHI
260 FOR I=6 TO 16:POKE DL+I,7:NEXT I
270 POKE DL+18,65
280 POKE DL+19,DLLO:POKE DL+20,DLHI
290 POKE 560,DLLO:POKE 561,DLHI

300 REM *** READ IN ASSEMBLY CODE FOR FLIPPING ***
310 REM *** STORE IN P6 MEMORY LOCATION 1536+I ***
320 FOR I=20 TO 50:READ DAT:POKE 1536+I,DAT:NEXT I

400 REM *** READ CODE FOR VERTICAL BLANK INTERRUPT ***
410 FOR I=1 TO 10:READ DAT:VBI$(I)=CHR$(DAT):NEXT I

500 REM *** SHORT & SWEET MAIN LOOP! ***
510 VBI=USR(ADR(VBI$))
520 GOTO 520

1000 REM *** CODE FOR PAGE FLIPPING DURING VBI ***
1010 DATA 198,203,208,24,169,30,133,203
1020 DATA 230,204,165,204,201,4,208,2,169,0,133,204
1030 DATA 165,205,24,101,204,141,5,6,76,98,228

2000 REM *** CODE FOR VERTICAL BLANK INTERRUPT ***
2010 DATA 104,169,7,162,6,160,20,76,92,228