[Coco] clever idea didn't work

[Mark McDougall]

On 19/12/2014 12:40 PM, Robert Hermanek wrote:

> Perfect, except:  The TV will not display the
> VGA signal, says "mismatch resolution."  But the manual for TV says it
> supports 640x480, 60hz.  I plugged converter into a normal vga monitor,
> worked perfectly, brought up the menu and it says 640x480 60hz. So.  Maybe
> TV doesn't support that res, and manual is wrong.  Or... could there be some
> other reason the converter output would not be recognized universally?

Monitors in analogue mode calculate their resolutions from the HSYNC count 
and/or HSYNC frequencies. There is no concept of 'pixels' so they are unable 
to discern different horizontal resolutions. So the '640' is assumed based 
solely on the HSYNC freq/count (480).

If the HSYNC frequency varies from the 'standard' for a particular 
resolution, then the output may have more/less scan lines in the vertical 
blanking period to make up for the 60Hz frame rate. It may be that the TV 
can't handle a slightly 'non standard' signal.

Other possibilities, though perhaps less likely, are oddities like the VGA 
converter not generating HYSNC during VBLANK, which can also confuse lesser 
monitors. TV's are notorious for being fussy about analogue signals.

My guess is that you're SOL. :(

Regards,

-- 
|              Mark McDougall                | "Electrical Engineers do it
|  <http://members.iinet.net.au/~msmcdoug>   |   with less resistance!"