With no CRT monitor connected to a pc the Hsync and Vsync pins will stay at
5V.
Power down , connect monitor , power up both and Hsync and Vsync drop to TTL
logic High but what is also required to make the pc send out sync pulses to
the monitor ? Do the DDC lines do more than identify the monitor type ? ie
if that data is absent will the pc not respond at all.

"n cook" wrote in message
...
With no CRT monitor connected to a pc the Hsync and Vsync pins will stay
at
5V.
Power down , connect monitor , power up both and Hsync and Vsync drop to
TTL
logic High but what is also required to make the pc send out sync pulses
to
the monitor ? Do the DDC lines do more than identify the monitor type ? ie
if that data is absent will the pc not respond at all.



More on DDC:

http://pinouts.ru/data/VGAVesaDdc_pinout.shtml