HP 9845 C with 280 option startup failure
ard at p850ug1.demon.co.uk
Fri Nov 11 18:45:28 CST 2005
> > Are you sure that doesn't also apply to the 98780 enhanced mono monitor?
> > The text and graphic systems are pretty much seperate on that monitor,
> > OK, there is one video timing chain (on the text PCB) that provides
> > timing signals to the graphics board too, but the graphics unit has its
> > own memory, video shift register, etc. The outputs are combinded by a
> > fairly complex mixer circuit on the interface PCB in the monitor. There
> > is no good reason why the 2 can't be displayed at the same time.
> Maybe you're right. In fact, although (according to the boardswapper)
> the 98780 and the 98770 have slightly different overall video timings,
> both use one single scan raster for alpha & graphics with just different
> viewable areas. This is not the case for the standard mono crt. So maybe
In the 98780, there is one video timing chain, physically located on the
text (alpha) PCB. It's the traditional chain of counters, decoded by AND
gates, used to control JK's to provide various timingt signals (you need
the schematics, OK :-))
Many of the signals are passed across the monitor backplane to the
procesor (graphics) PCB, but there is no complete timing chain on that
PCB. The only board that provides syncs to the analogue section is the
text PCB, and from what I rmember, tbere are no control inputs to that
timing chain depending on whether it's in text or graphics mode.
I was under the impression that the 98770 (colour) and 98780 (enhanced
mono) were pretty similar to the user apart from the obvious difference.
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