Clock

I made this small program to demonstrate the use of the ZX81's video generation routines in the implementation of a multi-task application, in this case a digital clock that is updated simultaneously to the execution of the BASIC program.

Provide time in HHMMSS format, with 24-hour count. The digital clock will be shown in the upper right corner of the screen as a square moves from side to side across the screen. Stop the BASIC program with BREAK and observe that the clock continues to update. Clear the screen with CLS or give a LIST, the clock is still there and is only deactivated with the commands FAST, LLIST, LPRINT, PAUSE or by editing a line in the BASIC program.