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From: Jon Jenkins <jenkinsj@ozy.dec.com>
Newsgroups: comp.unix.bsd.freebsd.misc
Subject: Re: Oddball Monitors
Date: 18 Nov 1995 06:18:47 GMT
Organization: Digital Equipment Corp
Lines: 238
Message-ID: <48jts7$i65@nntpd.lkg.dec.com>
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The following may be of some use
Jon
--
----------------------------------------------------------------------
Name: Dr Jon Jenkins Location: Digital Equipment Corporation NaC
Voice/Fax: 61-7-55-75-0151/100 Burnett Place, Research Park,
Inet: jenkinsj@ozy.dec.com Bond University, Gold Coast
Close Proximity: "HEY YOU !!!" QLD, AUSTRALIA 4229
"Daddy, what's outside the Universe?" (My 5 year old.....)
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Notes on VGA->RGB conversion:
Be warned some monitors (older SUNs in particular)
use RGB+CSYNC i.e. 4 connections and
not "sync on green" RGB. There may be a jumper inside
the monitor to change this but you should seek assistance
to make any changes of this nature. Alternatively
you can just take the CSYNC signal from below
and use it.
I have not blown up any monitors in my testing
but it is possible to blow up a monitors input
stage. If you are in any doubt get someone
who knows what they are doing to do these
alterations.
-------------------------------------------------
IF the video card you are using is a standard VGA output:
(Im using a Diamond stealth 64 VRAM but I have also
tested this on my wifes Tseng Labs SVGA card)
1: RED video
2: Green video
3: blue video
4: monitor id bit 2
5: Ground
6: red return
7: green return
8: blue return
9: NC
10: sync return
11: monitor id bit 0
12: monitor id bit 1
13: H sync
14: V sync
15: NC
I join all the "returns" together with the ground
on the small PCB and use that as a common ground
for the RGB cable to the monitor. You can use
separate if you want to but you should join the
green return and sync returns together. I did
find some small shadowing if I didn't group
them all together.
Just a note, when you set up your video card in Windows
OS/2 or whatever, set it to whatever is closest to the
monitors resolution as a first approximation.
My Diamond gives me a lot of freedom for adjustment
but some cards dont. As a general rule Workstation
monitors are not interlaced.
I use a DEC VR260 (1024x864@60Hz) at 1027x768@70Hz
or a VR319/320 (1280x1024@72) exactly as per the
setup menu.
Dont forget you CANNOT do 1280x1024 with a
1M RAM video card!!!
Note: Your standard VGA monitor may not like this
frequency so either disconnect it *VERY* quickly or
before you actually set the video card to the new mode
(i.e. put the OK as the active control in Windows and
then connect the "big" monitor and hit return). My
Diamond setup gives me 10 seconds to do adjustments.
When you exit you will probably have to select the
new mode with your old VGA connected again
but from then on every time you start Windows you will
be able to view it in "big" mode. Note the workstation
monitors are not multisync monitors so all you see
when you boot up DOS is garbage until Windows starts,
I put "win" in my autoexec.bat file.
If all else fails you can set the video
card to the closest resolution i.e.
1024x768 for a 1024x864 monitor and
and adjust the Hsync and Vsync frequencies
on the monitor. These may be accessible
from the outside either as dials or
by ***PLASTIC*** screwdriver access.
DO NOT ***REPEAT*** DO NOT use a metal
screwdriver for accessing these
recessed sync controls. Alterntively they
may be inside the monitors case.
****************WARNING***************
If you have to open up a monitor to do
this adjustment be warned: monitors have
very *LETHAL* voltages inside. You will not
get a second chance!!! Unless you know exactly
what you are doing get someone else who does
to do this adjustment.
****************WARNING****************
Note there is a danger here:
During testing I had set up the monitor and for some reason
it did not work so I couldn't see what was going on:
My ol VGA wouldn't work either either so I had to
find the cards .ini files and edit by hand to get
back to useable video !! Make a backup of the
video/system .ini files just in case this happens.
For FreeBSD/XF86 setup is trivial, the lines
for a DEC VR260 and a DEC VR320/319 using
an XOR (or an OR) gate are:
Modeline "1280x1024" 130.81 1280 1312 1472 1696 1024 1027 1030 1063 +hsync +vsync
Modeline "1024x864" 69.2 1024 1040 1168 1272 864 864 867 904 +hsync +vsync
For a NAND gate change the syncs tp -hsync and -vsync
See your monitor manual for the frequency,
porch and blanking details
-------------------------------------------------------
The circuit to do this is as follows:
Note.
1: you may be dealing with 135MHz sqaure waves so there
are lots of high frequency stuff around; use good
RF practices.
2: the coupling capacitors are a safeguard to start with
I dont use them cause they caused shadowing around
sharp colour changes (the ol RC effect).
3: Use the XOR gate first as a test but you may need
other gates to actually get it working
4: A CRO will be handy (necessary!) for final adjustment.
5: Make the device is as close as possible
to the video outlet on the VGA card.
6: Take the 5V from the PC power supply
inside the box. I just hooked one of the
spare connectors which I also use for an external
fan (5V pentiums being the heaters they are!).
Make sure (check it again!!) (and again!!!)
you dont get 12V else say "goodbye" to your monitor!!!
7: You must use a VN10KM or other
SMALL SIGNAL
N CHANNEL
ENHANCEMENT MODE
MOSFET
others will not work !!!!!!!!
+5.0V
|
/
\ VR1 (1k carbon mini pot)
33uF tantalum | ~0.3V DC in porch area
GREEN------|----||-----|--------------------|-----GREEN to monitor|
|----||-----| |
.1-.01uF ceramic |
|
gnd |
| |
/ |
\ 47k |
/ _|
HSYNC---|----|-------\ |
| GATE |------CSYNC----|----|| VN10KM or similar small
VSYNC---|----|-------/ / |_ N channel enhancement MOSFET
/ | \ |
\ / gnd
/ 47k \ 47k
| |
gnd gnd
HSYNC, VSYNC and CSYNC are grounded with 47k carbon resisitors
GATE=LS or HC types, HC preferred.
OR: logic is: when both syncs 0 the gate output
is 0 and the FET is off. When either or
both syncs go +ve the gate drives the FET on
which pulls the green to ground.
NAND: logic is: when both syncs are logic 1 the
gate output is 0 and the FET is off. When
either sync goes to 0 the gate output drives
the FET on and pulls the green output low.
This is the most common form of sync output
from PC SVGA cards hi res mode.
XOR: for -ve or +ve logic sync and hysnc during vsync
logic is: when both syncs are 1/0 the gate output
is 0 and the FET is off. When the Hsync changes
state the FET turns on pulls green to ground.
When the Vsync changes state the output is gated
by the Hsync and if your video card produces
Hsync during Vsync (most do) then the green
signal will be a square wave with a non 50% duty
cycle. Some monitors require this Hsync
action during Vsync otherwise the horiz
PLL loses lock.
Capacitors are optional, I dont use them now but
I used them during testing. They will cause a
shadow effect due the the 75ohm resistances
at either end of the circuit causing a DC bias
buildup on the green signal.
Get a CRO an adjust the variable
resistor so that the green levels to 0.3V
during video and 0.0V during sync pulses.
I used standard 74HC 14pin DIP gates
and 14pin DIP sockets originally so that
I could change gate types (OR/XOR/NAND) easily.
Good luck
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