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.