[net.micro.pc] screen flicker

markz@microsoft.UUCP (Mark Zbikowski) (08/31/84)

	When it writes to screen memory, I get colored static on my screen (I am
	using a IBM color display).

The IBM PC color card does not have dual-ported memory.  As a result, whenever
you are poking the memory at the same time the display controller is reading
it, it will read garbage due to the extra stuff on the bus.

To work around this, examine the ROM code in your IBM Tech Ref manual to
see how it waits for vertical/horizontal retrace before poking with things.
You will have 12 Microseconds for a horizontal retrace and 12 Milliseconds
for a vertical retrace.  If you need more time than these, you may elect
to shut off the video beam altogether (but you'll get an annoying flicker).

Remember, in you instruction timing calculations, to add the 1 wait state
for every memory fetch on the PC.

haapanen@watdcsu.UUCP (Tom Haapanen [DCS]) (09/07/84)

Tee hee hee hee

Hyperion gets no such snow on the screen ... and it emulates both the
monochrome and graphics cards.  The only thing I have found that won't
run is the Flight Simulator (but then, it can't even use a RGB display
with colours...)

Tom Haapanen
{allegra, decvax}!watmath!watdcsu!haapanen