Sync on Green FAQ


Chapter 5) How can I get a fixed frequency (RGB) monitor to work on my PC?

(Excerpts from comp.sys.ibm.pc.hardware.video FAQ)

(From Michael Scott and Bill Nott)

There are plenty of old RGB monitors (possibly from old Sun, SGI, or other workstations) around which are attached to outdated or non- functional machines. Most of these units are quality products by Sony, Hitachi or other vendors. You want an easy way to connect your VGA or better card to the monitor. It's may not be that easy, since many of these monitors are only capable of displayed non-standard pixel addressabilities, but read on..

The easiest solution (but not necessarily the cheapest) is a commercial solution. See the section from Declan Hughes, below.

Most of the old RGB monitors are fixed frequency, meaning that they are intended to work at only specific horizontal and vertical scan rates. This is in contrast to many newer models which are variations on the multi-sync theme. Multi-sync means that the monitor can sync to a RANGE of scan rates, or a number of discrete scan rates, based on the incoming video signal. i.e. the monitor will detect the scan rates of the video signal, and switch to the closest scan rate it is capable of. Since a fixed frequency monitor can't do this, you have to make sure that the video signal your video card is generating is compatible with the monitor.

To hook up a VGA card to a fixed frequency monitor requires three things:

  1. A cable that connects the VGA output to the RGB (and possibly sync) on the monitor. This may be the easiest part. Fixed frequency monitors typically have BNC connections for video input, so you need a cable which connects to your computer video output (typically a 15 pin D-Sub VGA) at one end, and which has 3, 4, or 5 BNC's at the other end. The number of BNC's depends on how you plan to resolve the sync signal issue (see point 3).

  2. The horizontal and vertical scan rates must be compatible. Some video cards have adjustable scan rates, and if you can adjust the video signal to be within the range that the monitor can handle, you might be in business. If you can't get the generated video signal scan rates to within the monitor's specs, you need a scan converter, which is a very expensive and complex device (read: not practical). Even if you can get your graphics controller to adjust to the monitor's unique frequencies, you will have to figure out what to do when you first boot your PC, and how to run DOS programs, if needed. Just about every PC boots up in the DOS character mode (720 by 400 pixels, 31.5 kHz Horizontal, 70 Hz Vertical). No fixed frequency monitor will operate at this mode. If you never need to use DOS, you may be able to set your autoexec.bat to start Windows immediately upon boot-up.

  3. You must have a compatible electronic signal. The problem is this: VGA cards have separate channels for red, green, blue, vertical sync and horizontal sync. Most RGB monitors have 3 or 4 connectors, either red, green (with sync) and blue, or red, green, blue and a separate sync. The sync signals from the VGA card must be combined to be fed into the monitor. This is not as simple as soldering the horizontal, vertical sync and green wires together. Some folks have been able to get their monitors to work by building simple circuits. However, keep in mind that items 1 and 2 above MUST also be satisfied. One such circuit that has been suggested is [below]. Unfortunately, I don't know who designed this circuit, so I can't give credit but it's part of the Apollo FAQ (included in the Sync On Green FAQ you're reading now!) It is presented as-is, and there are no guarantees that it will do what you need. Be warned, if you don't have considerable electronics experience you shouldn't attempt this. If you blow your monitor or video card, don't come crying to me.
(From Declan Hughes)

A frequently asked question is how to use a fixed frequency monitor (often a Sony or Sun monitor) with a PC AT. Three companies that provide the required video cards are:

  1. Mirage Computer Systems
    4286 Lincoln Blvd
    Marina Del Rey, CA 90292
    tel: 1-310-301-4541
    fax: 1-310-301-4546
    WWW: http://lainet3.lainet.com/mirage/
    E-Mail: Emil Darmo (mirage@lainet.com)

  2. Software Integrators
    104 East Main St
    Suite 206
    Bozeman, MT 59715
    Tel: 1-406-586-8866
    Tel: 1-800-547-2349
    Fax: 1-406-586-9145

  3. Personal Computer Graphics (PCG) Corp. (Photon)
    Tel: 1-800-255-9893
    Tel: 1-310-260-4747
    Fax: 1-310-260-4744
    WWW: http://www.photonweb.com/
    EMail: ben@photonweb.com

  4. MaxVision
    Tel: 1-800-533-5805 ext. 202

  5. STB
    WWW: http://www.stb.com
    FTP: ftp://ftp.stb.com/
Mirage make video cards that support all single frequency/high frequency monitors that operate between 28-35Khz, 47-52Khz, 60-65Khz and 70-78Khz at specific VGA, EGA and DOS modes (various drivers are included) with ISA, Vesa local bus & PCI local bus interfaces. They also have fast drivers for specific software products such as Autocad, 3D Studio and Windows 3.1 etc.

(From Michael Scott)

They have three models which use popular video chipsets:

Model                   Chipset         Max RAM         Bus
=====                   =======         =======         ===
Wind 1280s              ET4000W32P      2 MB            ISA, VLB, PCI
Storm 1600s-Pro         S3 64-bit       4 MB            PCI
Wind 1280s-Pro          ISLNG Viper 128 4 MB            VLB, PCI
Drivers are available for Windows 3.1, Windows 95, OS/2 Warp, ACAD, Linux, lots of CAD programs & VESA compatible applications. All cards support separate sync and composite sync as well as sync on green. Software comes with the cards to adjust frequency, setup and centering.

Mirage will give you a special discount if you mention that you were referred from this FAQ (No, I don't get anything in return :-( )

(From Declan Hughes)

For example, a STORM 1280/256 will drive a Sony GDM-1950 at 640x480, 800x600, 1024x768, 1280x1024 and DOS modes (this monitor is rated at 63.34Khz Horizontal sync. and the card runs at 64Khz Horizontal sync.). This card uses an S3 graphics accelerator. See also PC Magazine/April/13/1993.

Software Integrators make similar video cards (the MERCURY X1 Series) that will also support CGA modes as well as DOS, EGA and VGA modes using the S3 801 graphics accelerator and again they also make fast drivers for specific products such as Autocad, 3D Studio and Windows 3.1 etc.

These cards work with all fixed scan monitors including, IBM, Mitsubishi, Hitachi, Sony, Sun, HP, Verticom, DEC, Taxan, Philips, Apollo, Silicon Graphics, Intergraph, Aydin, Amtron, Monotronix, etc. and will replace old boards from, Artist, Number9, Nth, Verticom, Photon, BNW, VMI, Matrox, Metheus, Mirage, Graphax, Imagraph, TAT etc.

PCG provides several models, supporting ISA, VLB or PCI buses and their cards can support 1, 2 or 4 MB of video RAM. CL-5434 processors appear to power all of the Photon cards. They support sync-on-green (RGB) monitors, Windows95, Win 3.1, Linux and provide a variety of video drivers for various applications. Cards automatically boot up with a frequency compatible with your monitor.

For more information, refer to the Fixed Frequency PC Video FAQ at: http://www.wit.com/~xtian/video.html

All companies can supply interface cables such as a 15 pin male VGA to 5 BNC connector.

I have gleaned this information from sales sheets faxed to me, I am purchasing one of these cards, I am not related to either company, and both sales staff were very helpful (so please ask them for more detailed information).

I was also informed of a German manufacturer ELSA that makes similar cards, but I do not know of their address or product range.

(From Bill Nott)

Nobody has dealt with the radiated emissions issue. All PC's are marketed as FCC class B products. I recently learned that Mirage labels their cards as Class B. However, most of the single frequency workstation monitors becoming available are FCC Class A, and the FCC rules say that attaching a Class A device to a Class B system degrades it to a Class A system. This in itself is not necessarily a problem, unless the system is actually found by the FCC to be causing radio interference. My recollection is that the process of remedy for a Class A system is more severe than for a Class B system, so users may be opening themselves up to a higher level of risk. Comments are welcomed on this.

Chapter 6) Circuit for Converting from VGA to Fixed-Frequency RGB

ASCII file of a circuit which combines the vertical and horizontal sync signals from a VGA card with the green channel to give a red, sync on green, blue signal out. This circuit produces a signal that is compatible with many fixed-frequency monitors, but ensure that the signal you are sending has the same vertical and horizontal frequencies as the monitor expects.

For more information on how others have done this, read pertinent parts of this FAQ and refer to:

  6.1) Schematic 2

Some folks had concerns about the old circuit because it used an OR gate on the sync line. The next version of the FAQ will have the updated circuit which uses an XOR instead.

USE AT YOUR OWN RISK - Others have used this circuit but I have not!

From VGA card                                              To RGB Monitor
Red     1 O---------------------------------------------------------O Red
Blue    3 O---------------------------------------------------------O Blue
Green   2 O----------------------------------------------o----------O Green
                                            4066         |  Sync level adj.
                  ___________             ________ 4     |
                2 \          \            |   ___|_______|   __/\/\/\--O +5V
H sync 13 O--------\  74LS02  \  1      5 |   |  |  SYNC    _|_   ^
                    | (DIP)    |O------------>\  |         ////   |
V sync 14 O--------/          /   SYNC    |   |__|________________|
                3 /__________/            |      | 3
                                          |      |
                                          |   ___|___ *
                                          |   |  |
                                        * --->\  |
                                          |   |__|___ *
* tie to ground

Red     6 O-----------o---------------------------------------------O RGB
                      |                                         Cable Shields
Blue    8 O-----------o
Green   7 O-----------o
Returns              _|_
If no sync is present from the VGA card, pin 4 of the 4066 is in a high impedance state and does not affect the green video signal. If either horizontal or vertical sync is present from the VGA card, the positive sync voltage is gated onto the green video line. This "wire-or" of the signals seems to work!

I think that the video voltages presented by the VGA are a bit on the low side for the RGB monitor. It would be nice to have a video op-amp circuit to provide 1-3 dB adjustable gain on the RGB signal possibly using the NE592 video op-amps. The pinout for the 74LS02 is the more common one. Some flatpacks use pins 1 & 2 as imputs instead of 2 & 3. Use this circuit at your own risk. Good luck!

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