On Dec 16, 2008, at 3:20 PM, Michael Chaney wrote:
> > On Tue, Dec 16, 2008 at 2:58 PM, Ken Barber <[email protected]> > wrote: >> >> What it was, was sheer brilliance. Written by mathematicians at >> Cambridge, >> it was pure genius in its optimization of both hardware and code. >> For >> instance, there was no video card -- the processor generated the >> screen >> display and only ran its apps during the "blank" times between TV >> frames. > > I'm familiar with that, but my feeling is that it worked like the > Atari 2600 where the screen buffer was one scan-line, and the > processor would be interrupted at each scan. Not true of the ZX81 - the processor worked full-time outputting NTSC- compliant pulses to the video connector -- no real buffer in there at all -- and only ran commands during the blank spaces between frames. The processor's clock speed was "just right" to work with NTSC video. I knew that part of the ROM pretty well, since I wrote some machine code (NOT Assembler, mind you, but Machine Code! With my bare hands! Through the snow! You young-uns are so soft these days!) Back In The Day. You could take over from the ROM and send your own shapes, crude fonts, or whatever to the screen. Or you could shut off the video output completely so your programs ran more quickly. I always did this for my sorts (then, of course, turned the video back on when the sort finished). Ahh, you be bringin' back memories, laddie! I cut my teeth on one of those beauties. --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "NLUG" group. To post to this group, send email to [email protected] To unsubscribe from this group, send email to [email protected] For more options, visit this group at http://groups.google.com/group/nlug-talk?hl=en -~----------~----~----~----~------~----~------~--~---
