10 P%=&D00
   20 [
   30 OPT 0
   40 LDY#0
   50 .loop1
   60 LDA&7C00,Y
   70 PHA
   80 LDA&6000,Y
   90 STA&7C00,Y
  100 PLA
  110 STA&6000,Y
  120 INY
  130 CPY#&FF
  140 BNE loop1
  150 LDY#0
  160 .loop2
  170 LDA&7D00,Y
  180 PHA
  190 LDA&6100,Y
  200 STA&7D00,Y
  210 PLA
  220 STA&6100,Y
  230 INY
  240 CPY#&FF
  250 BNE loop2
  260 LDY#0
  270 .loop3
  280 LDA&7E00,Y
  290 PHA
  300 LDA&6200,Y
  310 STA&7E00,Y
  320 PLA
  330 STA&6200,Y
  340 INY
  350 CPY#&FF
  360 BNE loop3
  370 LDY#0
  380 .loop4
  390 LDA&7F00,Y
  400 PHA
  410 LDA&6300,Y
  420 STA&7F00,Y
  430 PLA
  440 STA&6300,Y
  450 INY
  460 CPY#&FF
  470 BNE loop4
  480 RTS
  490 ]
  500 MODE7
  510 FORA=0TO1
  520 VDU145,157
  530 PRINTTAB(7,A)CHR$(141)+CHR$(135)+"Demonstration of SCRNTOG"
  540 NEXT
  550 PRINT:PRINT"This is a machine code routine to copy  the screen into memory and memory back  onto the screen. This is particularly   useful if you are toggling between two  screens."
  560 PRINT:PRINT"It problaly has no real use because is  isn't very often you want to toggle     between two screens. But it is          interesting to see how quickly it can bedone."
  570 PRINT:PRINT"‘abcdefghijklmnopqrstuvwxyz1234567890"
  580 PRINT:PRINT"Press a key to use the routine"
  590 G=GET:CALL&D00
  600 CLS
  610 FORA=0TO1
  620 VDU146,157
  630 PRINTTAB(7,A)CHR$(141)+CHR$(133)+"The other screen!!!!!"
  640 NEXT
  650 PRINT:PRINT"This is the other screen by pressing    a key you can toggle between these two  screens very quickly."
  660 PRINT:PRINT"  To do this the screen memory from     &7C00 to &8000 is copied to &6000 and   and at the same time the memory from    &6000 is copied in the screen memory."
  670 PRINT:PRINT"To use this facility the second screen  must be set up and the the routine      called ie 'CALL &D00' and then the firstscreen can be set up."
  680 PRINT:PRINT"To toggle between the two the routine   is simply recalled ie 'CALL &D00'"
  690 PRINT:PRINT"Press a key to use the routine"
  700 REPEAT
  710 G=GET
  720 CALL&D00
  730 UNTIL0