VGA colour byte H&V sync bits

PatM

The colour white in VGA would be 11_11_11_HV

The higher six bits are colour information which is pretty easy to figure out. The horizonal and vertical sync bits are a bit more mysterious. I've tried setting them to both 1 and 0 and there seems to be no difference in the display. Do these actually have a function?

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RinksCustoms

I thought the sync bits were read-only, for the vga driver

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Mike Green

The sync lines are outputs from the Propeller to the display and are necessary to communicate the timing of the display information.

deSilva

To add a little bit more background:
The Propeller - in combination with a piece of software called VGA-driver which you are welcome to study - outputs within a not so complex timing scheme 5 signals to VGA monitor:

R,G,B,H,V

H and V are strictly digital and in need for the synchronization of lines and frames
R,G, and B are analogue colour data

The Prop however can output two bits for each color channel only: how this is transfered to the monitor is left to the board design; most boards "mix" those two pins by two resistors (R and 2R) - some hypocrats call this D/A converter...

So the 8 bits you describe become the 5 lines to the monitor.

Equal values of the color channels yield sorts of gray; when you used exactly the same resistor values this coresponds to 11_11_11, 01_01_01, 10_10_10, 00_00_00

But you can of course use a different "DAC" e.g. just using 1 bit for each channel, or use all 6 bits for a 64 level monochromious signal.

Post Edited (deSilva) : 7/11/2007 6:11:23 PM GMT