This utility contains 6 clear screen routines that will give your programs that special something they’re missing. The routines are a single 1,108-byte machine-code block at 64260. You choose an effect with two POKEs, to 23728 (0, 1 or 2) and 23729 (0 or 1), and then clear the screen with LET L=USR 64260 or RANDOMIZE USR 64260. The magazine notes that the code is not relocatable and does not touch the UDGs.
Credited to Eric and Kristian Boisvert, ©1987 Byte Power. Loading name CLS. Published on the Fall 1987 (Issue 8) tape of Byte Power.
Program Analysis
The BASIC part is a demonstration. After a title screen it fills the screen with inverse spaces (subroutine 1000) and, for each combination of d = 0–2 and c = 0–1, prints “CLS #n”, waits for a key and clears the screen with the selected effect. Line 9000 loads the code and runs the demo; line 9999 saves the BASIC and CODE 64260,1108.
Effect Selection
- #1:
POKE 23728,0: POKE 23729,0 - #2:
POKE 23728,0: POKE 23729,1 - #3:
POKE 23728,1: POKE 23729,0 - #4:
POKE 23728,1: POKE 23729,1 - #5:
POKE 23728,2: POKE 23729,0 - #6:
POKE 23728,2: POKE 23729,1
Notable Techniques
- The effect is passed in two bytes of the system-variable area (23728–23729) rather than in BASIC variables, so the routine can be called with a plain
USR. - Line 50 prints the credits in the lower screen with
PRINT #1. - Line 140 uses
RUNto restart the demo once all six effects have been shown.
Image Gallery
Note: Type-in program listings on this website use ZMAKEBAS notation for graphics characters.