Looking for a small fast VAX development machine

Mouse mouse at Rodents-Montreal.ORG
Sun Feb 28 07:52:52 CST 2016

> When I switched to a flat screen (after the CRT monitor died), the
> adjustment time was also the biggest disappointment.  As you mention,
> it usually takes 1, often even 2, seconds to recover after the
> blanking interval.

(Cognitive dissonance - "blanking interval" is a technical term in
video, meaning something inconsistent with your usage here.)

> What I can't understand is what causes the blanking interval.

Based on your description, I think this is happening whenever the
display is resyncing to the signal.  Unlike analog monitors,
flatscreens seem to do this largely in software (many of them even put
up some kind of user notification while doing it).  I think it happens
whenever the sync signal does something unexpected for the current
mode.  This can be a resolution change (since that entails a change of
at least one sync frequency[%]) or it can be a too-large phase glitch.
I suspect your 10% of the time when it doesn't resync corresponds to
switchings that don't change sync frequencies and happen to occur such
that the sync phase glitch is small enough to not trigger the
auto-readjustment.  My guess is that the host is re-initting the
display hardware, probably resetting sync to a top-of-screen.  If this
happens to occur close enough to the former top-of-screen, the sync
signal may appear close enough to uninterrupted for the monitor to
continue running without readjustment.

I may not be describing it well - but I don't see anything in your
description which is inconsistent with the theory in my head.

[%] In theory, a resolution change may not entail a sync glitch if you
are changing just the horizontal resolution, and you're changing the
pixel clock as well such that the horizontal scan frequency is
unchanged.  I suspect such changes are rare enough to "never" happen.

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