Xfig drawing EPS image
This document describes how to connect a Hewlett-Packard 98753A (or similar) monitor to your PC. There may be other ways; see the links section below.
Reassured? Ok, read on :-)
Since I didn't want to spend much on the cable, and had a length of 75 Ohm coax and some BNC connectors lying around, I made it myself. This allowed me to merge the sync signals in the VGA connector, as indicated in the figure below. By the way, all figures are available in Xfig and Encapsulated PostScript formats as well.
I hope it's clear from the image that you should solder the red, blue and green coaxial cables to pins 1, 2 and 3 of the VGA connector, respectively. The shields should go to pins 6, 7 and 8. Place BNC connectors on the other ends.
If you can get your video hardware to produce sync-on-green pulses, you're almost ready. You can find out more about this in the documentation of your X server (most likely in /usr/X11R6/lib/X11/doc/). Does your card support sync-on-green? Rejoice, and skip to the Modelines section.
If your card cannot supply the sync pulses on the green channel, you must deliver them to the monitor yourself. Does your monitor accept the sync signals on separate BNC sockets? Congratulations, you won't have to open it. If it has two sync sockets (they should be clearly marked), a ready-made VGA-to-BNC cable will do fine. A self-made cable will need two extra leads for the horizontal (pin 13) and vertical (pin 14) lines.
If the monitor has one, so-called composite sync input, you will still need to merge the horizontal and vertical signals. If you are making your own cable, you can do this by connecting pins 13 and 14 in the VGA connector using 100 Ohm resistors. In this case you only need one extra coaxial cable to the monitor, with its shield connected to pin 15. If you use a prefabricated cable, it will probably have an extruded VGA connector that you can't open without destroying. You can cut off both sync plugs and add the resistors at this end of the cable. Insulate with shrink tubing and reconnect one BNC connector. Ready.
Do you have an original HP98753A monitor without any sync inputs? In this case you can either merge the sync signals inside the cable (at either end, read the previous paragraph), or in the monitor. If you chose to merge them in the monitor, probably because you've got a ready-made cable you don't want to harm, you should add two BNC sockets to the rear panel of the monitor. Otherwise one will be enough. Yes, you have to open the casing, but I guess you won't find it hard to do. Remove the metal panel that already holds the red, green and blue sockets. You can even disconnect the coaxial cables on the other side; this is amazing, Mike! Drill one or two holes, in line with the existing sockets, and insert the extra socket(s).
If you added two BNC sockets, connect their center contacts with the 100 Ohm resistors you couldn't (or didn't want to) place in the cable. Solder a final piece of coaxial cable to the midpoint. If you added only one socket, this is the starting point for the last piece of coax. Make sure it's properly gounded, and run it alongside the red, green and blue cables.
Now for the hardest part, which I call `sync injection'. You must locate the exact point where you should connect the other end of the sync cable. In general, the circuit will look something like this:
That is, the red, green and blue channel each have their own video amplifiers, while only the green channel is connected to a sync-separating circuit. We should inject the sync signal there where it will not interfere with the video signal (for example, changing the black level). The above image shows how this can be done. The corresponding section in a HP98753A monitor is shown in this figure:
Since there is a 100 µF capacitor in series with the green line, you should also put one in series with the sync line (Cx). It doesn't hurt to use one with a higher rating than 10 V, but mind the polarity. Initially, you can probably do without Rx, so just connect Cx to the base of Q417. Later, you may find that the top lines of the image are shifted somewhat to the left or right. In that case, you may want to add a resistor. Using a 10 KOhm variable resistor, you should be able to correct this effect. (Why the uncertainty? It was not necessary to add Rx in my monitor, while my friend's needed a few K.)
This concludes the hardware part. If you feel really confident, you can close the monitor. I'd leave it open until everything works, though... Just be sure nobody pokes anything in while it's switched on.
Both SVGATextMode and X require a modeline - fortunately they accept the same format. Since we're dealing with a fixed frequency monitor, one modeline is enough for everyone (somebody once said something similar about 640 Kb :-)
From blh@hpuerca.atl.hp.com (Bill Hassell)
Organization the HP Response Center, Atlanta
Date 8 Sep 1997 03:04:44 GMT
Newsgroups comp.sys.hp.hpux
Message-ID <5uvq0c$8tk@hpuerci.atl.hp.com>
References 1
magne@inni.no wrote:
: Does any know if it is possible (with an adapter perhaps) to
: connect the monitor of an HP9000/710 to the vga(15-pin) output
: from a ibm-comp.pc? How does the output from the HP look like?
: Is it separate connectors for RGB, or one plug?
Timing summary for HP-Workstation monitors
All of the HP workstation monitors shown below for a given resolution and
refresh rate (such as "1024 x 768 at 60 Hz) will use the same timing. For
many monitors, there were A or B models, most often signifying Northern or
Southern hemisphere design...the letter x signifies A or B as in A4033x
means A4033A or 4033B. In addition, the following signal/input
specifications are common to all:
1. Input connectors and impedance: Separate BNC connectors for Red,
Green, and Blue. 75 ohms impedance.
2. Signal levels: Signal levels per EIA standard RS-343A; white
positive. Composite sync to be supplied on the
Green signal only (Note: horizontal sync pulses
need not be supplied during the vertical sync
pulse.)
(Note: horizontal sync pulses need not be
supplied during the vertical sync pulse.)
3. Timing
All signal timing is +/- 5%.
98782A/98751A/98753A/98785A/98781A/98786A:
Normal Field: 1024x768x60 Hz @ 64.1088 MHz dot clock
98784A/98752A/98754A/98789A:
Normal Field: 1280x1024x60 Hz @ 108.181 MHz dot clock
A1497x/A2287A:
Normal Field: 1024x768x75 Hz @ 84.587 MHz dot clock
98774A/A1097x/A2088A/A2094A/A4032x/A4033x/A4330x/A4331x:
Normal Field: 1280x1024x72 Hz @ 135.000 MHz dot clock
(only A433x and A403x monitors are multisync)
1024x768 1280x1024
60 Hz 60 Hz
--------------------------- ---------- ------------
Horiz. sweep freq.: 47.7 kHz 63.34 kHz
A. Horiz. period ("1H"): 20.96 us 15.788 us
B. Horiz. "front porch": 1.00 us 0.407 us
C. Horiz. sync width: 2.00 us 1.701 us
D. Horiz. "back porch": 2.00 us 1.849 us
E. Horiz. active scan: 15.97 us 11.832 us
F. Horiz. blanking: 4.99 us 3.956 us
Vertical frame rate: 60 Hz (non-in.) 60 Hz (non-in.)
G. Vert. active period: 16.097 ms 16.167 ms
J. Vertical blanking: 0.570 ms .505 ms
K. Vertical period: 16.667 ms 16.672 ms
L. Vertical "front porch": 62.89 us (3H) 47.36 us (3H)
M. Vertical sync width: 83.86 us (4H) 47.36 us (3H)
N. Vertical "back porch": 419.20 us (20H) 410.49 us (26H)
1024x768 1280x1024
75 Hz 72 Hz
--------------------------- ---------- ------------
Horiz. sweep freq.: 62.936 kHz 78.125 kHz
A. Horiz. period ("1H"): 15.888 us 12.800 us
B. Horiz. "front porch": 0.756 us 0.474 us
C. Horiz. sync width: 1.513 us 1.422 us
D. Horiz. "back porch": 1.513 us 1.422 us
E. Horiz. active scan: 12.105 us 9.482 us
F. Horiz. blanking: 3.783 us 3.318 us
Vertical frame rate: 74.924 Hz(non-in.) 72.005 Hz (non-in.)
G. Vert. active period: 12.202 ms 13.107 ms
J. Vertical blanking: 1.144 ms 0.780 ms
K. Vertical period: 13.346 ms 13.887 ms
L. Vertical "front porch": 63.55 us (4H) 38.400 us (3H)
M. Vertical sync width: 63.55 us (4H) 38.400 us (3H)
N. Vertical "back porch": 1.016 ms (64H) 704.00 us (55H)
Older HP workstation monitors are not PC compatible. The sync is provided
only on the green signal which most PC video cards cannot provide. They are
also fixed frequency and while an appropriate Windows driver might provide
the right display, you would see nothing during power on selftest or DOS
activities. In fact, running the monitor at the wrong frequency for an
extended period of time may damage the older circuitry.
For PCs, you will need a special video card that does not change frequency
at power-off or reboot and provides the sync-on-green signals. Check the
following URLs for some solutions to use an older single frequency HP
workstation monitor as a PC compatible unit:
http://www.photonweb.com/564-64/
http://www.mirage-mmc.com/hp.htm
http://http://www.si87.com
http://www.maxvision.com
Of the above monitors, only the A4032A, A4033A, A4330x and A4331x
are multi-frequency and therefore satisfactory for use with a PC. You
will need a VGA-to-5 BNC cable for 403xx monitors to provide the separate
sync signals. These cables are commonly available at PC dealers.
--
__?__
/ \
/ ^ ^ \
( (o) (o) )
\ /
*=oOOO======(_)=====OOOo====*=====================================*
| Bill Hassell | Hewlett-Packard Response Center |
| System Administrator | blh@atl.hp.com / Atlanta, GA. |
*=============Oooo.=========*=====================================*
.oooO ( )
( ) ) / "There are two types of computer users in the
\ ( (_/ world...those that have lost data, and those
\_) that are going to." (blh, circa 1972)
Thank you, Bill! I hope you don't mind this lenghty quote... I'm sure it has helped a lot of people. From the information in the column `1024 × 768 @ 60Hz' we can deduce the following modeline:
Modeline "1024x768" 64.109 1024 1088 1216 1344 768 771 775 795 -hsync -vsyncSo that's a 64.109 MHz dot clock (pixel clock), 1024 × 768 resolution, 60 Hz frame rate, non-interlaced, with negative sync polarity. Just to clarify this a bit, I've drawn the following image:
If you want to know more about this, please read VideoModes.doc in your local XFree86 documentation directory. For your information, I have included my /etc/TextConfig and /etc/XF86Config files. S.u.S.E. automatically runs SVGATextMode (stm) if /etc/TextConfig is readable, which means that I cannot see the boot messages. Alternatively, you could use xdm. You will probably find that the maximum text mode clock is not nearly as high as the maximum graphics clock. I wonder whether video card developers have ever seen a large and stable, high resolution text mode screen. It would certainly change their minds... or maybe marketing won't let them.
Finally, I must admit I haven't been entirely honest. I can see the boot messages... if I turn on the old VGA monitor. I have made an automatic switch, which reacts to the horizontal sync frequency. Three DIL reed relays direct the red, green and blue signals to the correct monitor. Since this is only a quick hack, it may not work for you. Suffice it to say that it has a 555 monostable triggered by the horizontal sync, an RC filter and a CA3130 as a level comparator. Not sophisticated, but operative.
You'll see that these documents contain a lot of links to related material, even to each other. Some of the links are outdated... It's the same everywhere. That's why you are free to mirror this page and its images on any archive: it will remain available, even if one of the sites shuts down. Now that's open source! Please send any remarks and suggestions to the address below.
