🚀 go-pugleaf

In article <3061.2...@cc.helsinki.fi>, mnyk...@cc.helsinki.fi writes:
> In article <ben.2630@epmooch.UUCP>, ben@epmooch.UUCP (Rev. Ben A. Mesander) writes:
> > If memory serves me right, the old Commodore PET machines could be
> > physically damaged (ie smoke) by poking the wrong value into the wrong
> > memory location. Good design...
> The original PC could control the voltage going to the monitor, I've
> heard, with similar results..
> -- 
> Matti Nyk{nen			CS Student at Helsinki U, Finland

Close, Matti, but no cigar.  (But the smoke was indeed there.)

The PC display adapters (all of them) can AND MUST generate a sync signal
at the sweep rate that the monitor expects.  This rate is software-adjustable.
When you call the BIOS function that sets the video mode, that's one of the
things the BIOS code does.  But if you're brave and knowledgeable, you
can do it from your own ASM program.

Well, the original IBM monochrome monitor (not the PC itself) had a
sweep circuit that was NOT free-running; if it didn't get sweep sync
signals from the PC often enough, it just sat there pumping current
into the deflection circuits.  Leave a large current like that on
long enough and the deflection circuit generates blue smoke  :-(

OK, so if your ASM program that sets the sweep rate screws up and
sets the rate way too low........

Dave