Wed Jun 3 14:43:47 CEST 2009

TTL video

Time to get the hands dirty.  Too much programming and thinking
lately..  Here's one of the things I'd like to do.  I have 2 or 3 old
TTL monochrome monitors that I'd like to give a new life.  The pinouts
are in [1].

This could use the approach I used before for TV, but with syncs on
separate lines.  I used the SPI output port for sending video data.
On a 452 this i pin 24 (RC5/SDO).

The D-SUB Female:

5 4 3 2 1
 9 8 7 6

8 HSYNC positive
9 VSYNC negative

Let's start with connecting VIDEO to the SDO, and the hsync/vsync to
two other ports.  I used RA4 for Composite.

Ok, sending out stuff on SDO gives some signal.  Let's figure out

The horizontal frequency is supposed to be 18.43kHz.  That's 542 ticks
of a 10MHz clock.  The divisor should thus be 137 * 4.

Ok. Hsync works with a pulse of about 1.5 us wide.  It would be nice
to be able to get at some timing data to see how the vsync works
(duration and nb of lines..)

[1] http://pinouts.ru/Video/mono_ttl_pinout.shtml
[2] http://en.wikipedia.org/wiki/Color_Graphics_Adapter
[3] http://en.wikipedia.org/wiki/IBM_Monochrome_Display_Adapter
[4] http://www.seasip.info/VintagePC/mda.html
[5] http://en.wikipedia.org/wiki/Motorola_6845