Converting monochrome video signal to VGA monitor? - test-drb@ccmp.vtda.org

15 Jan 2008

Hi,

On Fri, 11 Jan 2008 "Martin Bishop" wrote:
...
  IIRC someone suggested using a multisync monitor, that
is likely to be
 the cheapest and simplest way ahead.  SyncOnGreen to Grn should give
 you a nice green greyscale - white would require a video buffer (the
 problem is loading by the terminators - which might just be
 switchable / linkable).  However UK prices for 19" NEC MultiSyncs are
 about 200, i.e. double the price of cheap TFTs.  Perhaps you can pick
 up a small second hand one.

 Boxes are available to convert RGB to VGA, see e.g.
 http://www.cadesigns.co.uk/mi1a.htm.  Not cheap, just slightly less
 than a multisync monitor, but the target market is banking.  I have
 used these for (VaxStation) VCB02 (RGB) to (VGA) TFT conversion.
 Although the Hz fit of the screen image can be a bit "iffy" -
 infinitely better than working on the console port.

 If you wish to roll your own, which I'm certain you don't, the
 Intersil EL4583 data sheet and associated apps notes are a good place
 to start.  Additionally, the apps notes contain a fair bit of
 background information which may be of interest. 
Thanks for the tip. Luckily it seems the video converter board I want to
use has separate TTL-level horizontal & vertical syncs, just like VGA.

I still need to determine the video signal amplitude, but it's looking
like I'll just be able to use a resistor to connect it to the green line
of the monitor. My monitor has 5 BNC inputs and can be set to high-Z,
but I'll be running it through a KVM switch which has normal VGA
connectors. The KVM probably has on-board termination. The amplitude
probably isn't sufficient to drive 75-ohm red, green and blue lines
without buffering/amplification.

Horizontal sync frequency will be around either 31kHz or 54kHz depending
on the mode (pixel clock 49.5MHz or 72MHz), so most modern (CRT)
monitors should be able to handle that. Interestingly, looking at the
board circuitry there seems to be a facility to provide your own pixel
clock, so the horizontal & vertical frequencies could be adjusted if
necessary. (Or maybe that was only used for factory testing.)

-- Mark