Flicker-free Four Times Normal Character Scrolling

Programming an active display without the flicker and flash is one of the challenges confronting the ZX80 user. So far the programs published in SYNC with flicker free display possibilities have some limitations: 1) the program must stay in machine language; 2) all computing must be done during the vertical blacking period; or 3) everything must be timed just right. We have had lateral scrolling for one line, but this scrolling is not suitable for a billboard because it is hard to read at a distance. Another program would display a message in characters eight times their normal size, but not enough information can be displayed on the screen at one time.