The 25 MegaHertz clock of the processor
is divided by 4 giving so 6.25 MHz used as pixel time unit. The
VGA frame is in refreshed with a 50 Hertz frequency and cut in
312 lines. Frequency lines is so 15.6 KiloHertz.
A simple calculation allows to determine
the total clock cycles number by line to 6.25 MHz are 6250000/15600
= 400 (after roundness).
The various timings can be defined
in the following way:
The signals of synchronization line and frame are negative
(0 during the duration of the pulse). Only one synchronization
signal must be created wich is the exclusif or of line and trame
Here is the wiring plan between mini-control board VGA connector
and TV peritel connector: