Silicon Graphics / IRIX 13W3 and Sync on Green (SoG) solutions

Elf

Storybook
Feb 4, 2019
252
57
28
The first thing that people often come across when using older SGIs is the 13W3 video output. The one and only solution I recommend to this is the famous "DIP switch" cable that adapts from 13W3 to a standard HD-15 VGA connector. This cable is in current production by cablesonline.net, and can be found on eBay here (for $20): 6 ft. 13W3 Male to SVGA (HD15) Male Universal Cable w/ 12 Dip Switches - W3-606. Note that via the DIP switches it supports configurations for SGI, Sun, and IBM (and presumably others), so if you own other old UNIX workstations with 13W3 outputs this will be a very flexible cable for you.

s-l500.jpg Screen Shot 2020-03-02 at 8.36.45 PM.png

The cable itself appears to connect through different pins based on the DIP switch setting, and has some ability to route sync around to use either composite, H/V, or Sync-on-Green (SoG) outputs. It is not clear to me whether there are any active electronics in the cable and whether it is performing full SoG conversion or simply duplicating signals to other pins to get a SoG capable monitor to do its thing.

Although the easiest thing to do from here is simply to use a SoG capable monitor (with DIP switches set as per the SGI H/V sync out column), people will occasionally run into (or simply already have) monitors that they like that do not handle Sync on Green properly. I have come across something that seems to be a decent solution to this as well.

"Sync stripping" equipment can be used to separate the sync signal from a Sync on Green output and also remove it completely from the green channel. Sync stripping devices can range from small and cheap to large and professional. I've been playing around with the Software Integrators 7053 Sync Separator. Some of these can currently be found for fairly cheap (less than $20) on eBay, so if you want one, snap one up while you still can!

The 7053 Sync Separator will translate a sync-on-green RGB analog video signal to a standard separate sync (VGA) signal.
Sync-on-green is typically output from all DEC, NeXT, HP, SGI, APOLLO, and IBM workstations.
[...]
Green Video
  • Output pin 2
  • Sync signal removed
  • 75 Ohm Source Impedance
  • 0.0 to 0.7V DC Coupled
I have paired up this device with the 13W3 cable (with DIP switches set to SoG output) and it does appear to output proper H/V sync with no more SoG signal, as advertised.

Note that the 7053:
  • Requires a center positive 6V 5.5x2.1mm DC barrel jack power input (missing from the current eBay listing)
  • Has a male input and a female output. This leaves it the wrong way around for connecting on the end of the 13W3 adapter cable, and you will need both M/M and F/F gender changers to reorient it. If you do not, you will simply not see any signal!
SI 7053.jpg DIP 13W3.jpg

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Screen Shot 2020-03-02 at 8.26.39 PM.png Screen Shot 2020-03-02 at 8.26.51 PM.png Screen Shot 2020-03-02 at 8.29.41 PM.png
 
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Reactions: LarBob

LarBob

Administrator
Feb 8, 2019
28
10
3
Awesome! I've been thinking about trying this for a while in order to be able to screen capture SGI machines much more cheaply as well.
 

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