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On Thu, 10 Mar 2005, Chris Wilkson wrote:
> > -- video sync output
> > process (posNOW)
> > begin
> > if posNOW = "00010000" then -- 00010000 == 16
> > sync <= not ('1' xor regVSYNC);
> > elsif posNOW = "00100000" then -- 00100000 == 32
> > sync <= not ('0' xor regVSYNC);
> > end if;
> > end process;
> >
> > Did I get the logic levels right? Ack, I still don't feel
> > like I'm on solid ground here.
>
> When regVSYNC is a one, you want the pin to be high during hsync
> and low otherwise.
> So you need to invert your counter logic:
>
> sync <= ('0' xor regVSYNC); -- turn on hsync
> sync <= ('1' xor regVSYNC); -- turn off hsync
isn't
sync <= not ('1' xor regVSYNC);
equivalent to
sync <= ('0' xor regVSYNC); -- turn on hsync
?
method one... when regVSYNC = 0, sync = 0
when regVSYNC = 1, sync = 1
method two... when regVSYNC = 0, sync = 0
when regVYSNC = 1, sync = 1
Well color me silly. Doesn't this then become...
-- video sync output
process (posNOW)
begin
if posNOW = "00010000" then -- 00010000 == 16
sync <= regVSYNC;
elsif posNOW = "00100000" then -- 00100000 == 32
sync <= not regVSYNC;
end if;
end process;
- --
adam@xxxxxxxxxxxxxxxx http://cuddlepuddle.org/~adam
KG6GZR http://cuddlepuddle.org/~adam/resume.html
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