Screen Wrap-A-Round

SCREEN WRAP-A-ROUND


by Mark Turner





It might (to the untrained ear) sound a bit boring, but type in Mark's


first program and you're sure to go into spasms of rapturous joy. What


it does is take the middle third of the screen and spin it round as if


it's drawn on a cylinder. Useless? Maybe. Jolly good fun all the same?


Definitely.





As with all this month's programs, getting it going involves the


time-honoured routine of typing in the first Basic section, saving it


onto a blank tape and then using the Hex Loader to enter the hex part,


which is then saved after the Basic. Hopefully there's room for a copy


of the Hex Loader this month as I don't think it's appeared for a


while. Remember that you only want to type in the letters and numbers


in the hex dumps (not the spaces which are only there to make things


clearer) and when you reach the end press Symbol Shift and A to stop.





When you reload the program its built-in demo routine will show you


exactly what's going on. Study it closely and you'll see that you need


to repeatedly RANDOMIZE USR 64750 to get the scrolling to work. (It's


in Line 100 - see?) The program sets aside 2048 bytes of memory to


store the bit of screen being scrolled. This is initially at address


62050, but you can change it by POKEing 64990 with something else.