Well, sorry that I took so long to respong this time.  (Exam time, you
know? :) )  ANyway, I looked at my SFB, and the second crystal seems to be
at the frequency of a PMAGB-BC (i.e. 69.1968 mHz) even though it is
labeled (on the outside) and calls itself a PMAGB-BA.  Shouldn't this
work then?

More confused than before,

=====================================================
J. Alexander Jacocks	Systems Administrator
			National Institutes of Health
			NIH/DCRT/CFB/EASS
silence@wam.umd.edu	alex_jacocks@nih.gov
=====================================================

On Mon, 1 Dec 1997, David Burren wrote:

> On Fri, 21 Nov 1997 13:06:23 -0800  Jonathan Stone wrote:
> 
> > Can you get the model number (like VR-2xx, or VR19) from the back of
> > the monitor and post it? and also the output of
> > 
> > 	>> cnfg
> > 
> > with the model number and any version/submodel info of the PMAGB-BA?
> > (>> cnfg N, where N is the slot with the sfb, might have more info.)
> 
> Open up the box and find out the speeds of the two oscillator cans on
> the card, and the state of the oscillator-select jumper (described
> further below).
> 
> > I seem to remember that the SFB actually comes in two varieties, which
> > run at different video rates (60 and 66 Hz, or possibly 66 and 72).
> > But the driver in NetBSD only seems to use one speed. Perhaps you have
> > a monitor/card combination that Ultrix supports but NetBSD doesn't?
> 
> Simon Burge wrote:
> 
> > We've also got a number of SFBs here with an extra 60 something MHz
> > crystal so that they can drive monitors like VR297s at 1024x864 (you
> > select between the two crystals with a jumper).  I think the "offical"
> > part number for one of these is a PMAGB-BC, but we just modified the
> > PMAGB-BAs ourselves.  Maybe that could be a problem too.  This is where
> > the `>> cnfg N' will help greatly - the SFB spits out all sorts of info
> > when queried.
> > 
> > I _think_ that PMAGB-BBs could drive 72 & 66 Hz, and PMAGB-BDs could
> > drive 72 & 60 Hz.  This is stretching the memory somewhat!
> 
> The SFB chip works with a wide range of clock speeds.  If you read the
> original SFB paper from Digital:
> 
>   ftp://gatekeeper.dec.com/pub/Digital/WRL/research-reports/WRL-TR-93.1.ps
> 
> you'll see a _large_ range of clocks listed.  Based on the speed it
> autoconfigures to various resolutions (although the software/firmware
> needs to be able to understand what it's doing :-).
> 
> The PMAGB-Bx has a 130.808 MHz oscillator soldered onto the board, and
> a socket for another (selected by a jumper near the crystals).  This
> matches the VRT19's "hi-scan" rate (1280x1024, 72 Hz).
> I think this also works with the VR-320?
> 
> In the PMAG-BA the 2nd crystal is 119.84 MHz. This matches the VRT19's
> "lo-scan" rate (1280x1024, 66 Hz). 
> 
> In the PMAG-BC it's 69.196 MHz (the same oscillator used on the PMAG-B). 
> 
> As Simon says, if you have any surplus PMAG-B boards you can desolder
> the oscillator and install it in a PMAG-Bx.  When I did this (at the
> site that Simon & I worked at together) and told Digital about it, they
> went away and checked their documentation, and eventually came back
> saying that yes the cards were now PMAGB-BCs...
> 
> Be aware that you can't remove the 130.808 MHz oscillator - the card
> uses this to judge the speed of the 2nd oscillator.
> 
> You'll notice that the card itself only says "PMAGB-B", not -BA/-BC/etc.
> 
> Hmmm, I've just found a card with a 74.397 MHz crystal on it.  Hadn't
> noticed that before...  Here's the list from the Digital paper:
> 
> 	Typical usage	Resolution	Refresh		Dot clock
> 	VGA		640x480		60		25.18
> 	VGA		640x480		72		32.00
> 	SVGA		800x600		56		36.00
> 	SVGA		800x600		72		50.35
> 	1K VGA, ACE	1024x768	60		65.00
> 	1K VGA, ACE	1024x768	66		66.00
> 	1K VGA, ACE	1024x768	72		72.80
> 	1K VGA, ACE	1024x768	72		74.37
> 	Digital		1024x864	60		69.20
> 	Sun		1152x900	66		92.98
> 	Sun		1152x900	72		104.00
> 	Digital		1280x1024	66		119.84
> 	Digital		1280x1024	72		130.81
> 	Digital internal 1600x1200	76		219.00
> 
> Getting hold of some oscillators at appropriate speeds and experimenting
> to find out which ones work with the PMAGB-B could be an interesting task.
> 
> I don't have time to do this, but if anyone wants to take it on I will
> offer one PMAGB-B card as a reserve (just in case you're nervous about
> blowing up your only PMAGB-B...).
> __
> David Burren
>