Re: help with VGA timings

Jordi wrote:
Hi,
I'm new in fpgas.I've been researching about vga timings for a few
days, but all information I've found it's confusing. I will try to
explain what I've learn:

HS,VS signals are active low. HS tells the monitor to begin a new line,
VS tells the monitor to begin a new frame. Before activate HS ,monitor
must be in blanking mode (front porch),before draw another line monitor
must leave blanking mode (back porch). The same for VS. There is an
active time to draw all line pixels.

I'm correct?

HS & VS are not necessarly active low, it depends of the mode. Note that
all recent monitor I tried absolutly didn't care about polarity and
locked what ever I used ...

You have :
* Front porch : Sync signal is not active, video signal is at blanking
level
* Sync : Sync signal is active, video signal is at blanking level
* Back porch : Sync signal is not active, video signal is at blanking level
* Active video : Sync signal is not active, video signal is whatever
you need to display

and that's for both h & v sync.


I don't understand timing.
For example if back porch takes 4us and active time takes 25 us in a
640x480 screen

Is the monitor expecting this timings? I mean , if I stay 8 useconds in
back porch will the monitor wait for me? , or will it begin to draw the
line after 4us?

Is the monitor reading RGB data every (25us/640)?

The monitors try to "lock" onto the input signal ... depending on the
monitor a particular signal might be recognized or not ... The only way
to ensure it's gonna be recognized by all monitor is to use a "standard"
timing. If it's just for experimentation, just try ... it might just
work ...


Sylvain
.

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