Identifying video signal by oscilloscope diagram

[Vein]

Hello

I have an issue with identyfying video signal on Megatel SBC, documentattion for this board is non-existant, so I used for newer board datasheet, but it does not match fully (lightly speaking...). I have done some tests, and on (theoreticall) h-sync, v-sync and green signal recieved this kind of output as on pictures
Can anyone somehow can help me out in identification?

 

[Hugo Holden]

The middle image you posted (presumably a two channel recording) could be showing a negative going V sync or drive pulse and positive going H pulses.

The V sync or drive pulse is often a regular pulse at close to a 60Hz fequency, The H pulse depends on the output standard to suit the VDU and it could be around 15.7kHz for CGA, around 18kHz for MDA and 21.5kHz for EGA and 31.5kHz for VGA and in VGA the vertical frequencies can be higher too. EGA has a reverse polarity V sync pulse compared to CGA, so a VDU can identify it and auto switch scan modes.

I'm not sure what VDU a Megatel SBC would drive, if you could find that out you could look at the standard for the VDU and try to find those pulses on the SBC's output connector.

I guess its possible that the SBC has a composite video out, where you would find the H&V syncs (both negative going pulses) mixed together, with the picture information (text & graphics etc) going positive in the active scan time between the pulses. In this case in the un-terminated condition the voltage is around 2 Volts peak to peak, and settles to about 1 V peak to peak when terminated with a 75 Ohm resistor.