Frequency monitor and switcher... How to?

[xnihilo]

I would need to use a CGA arcade monitor on a PC computer (with VGA output).
The arcade monitor is normaly fed with 15KHz signal horizontal synch while a standard PC monitor is fed with 31Khz horizontal synchronization signal (negative polarity).
When my PC boots and until the right driver (arcmon.sys) is loaded in config.sys file, the output sync freq from VGA card is 31KHz which is harmful for the arcade monitor.
I would need a simple PIC 16f684/690 program that would sense the frequency it receives on an input pin from the VGA card (signal is analog 0.7vpp) and divide (roughly) the signal in two and output it until it receives a 15KHz output and then output it as is, or better, amplified to 4vpp.
I don't wish to reinvent the wheel, so I'm asking if anyone know if such code is available.
Thanks for any help you could bring me.
Happy christmas.

[malc-c]

Plenty of VGA to CGA converters on the market

http://cgi.ebay.co.uk/Arcade-VGA-to-...b3b0a3ff442aa2

for example

[xnihilo]

Yes, sure, but for what price.
I could use a LM1881N to get sync from composite video but I'm not sure RGB out and composite video are enabled at the same time on the VGA card. moreover, the level will still be 0.7VPP