1. Software does the job. Minimun hardware is needed

My goal in this project was to move the control of the rendering system entirelly to software.
Software handles everything, from syncronization pulses and clocks to the actual ouput of data.
What you need basicaly is 2 pic16f877a ( 40 pins ) , 2 small resistors , and a 20Mhz resonator/crystal

2. Why two microcontrollers?
Well , for speed. The thing works like nvidia's SLI. You get 2 separated processing units , that cooperate to get
the graphics drawn ( or calculated ). With a 20Mhz crystal and with the pic16f877a having 4 CPI ( cycles per
instruction), i can squeeze about 5 MIPS ( million instructions per second ) out of it, which is very low for our
purpose. Every scanline last for about 52us (microsecond) and during that time if the pic does nothing else other
than to draw a pixel on the screen using 2 instructions per pixel ( one to get it and one to draw ), it can draw about
100 pixels. But that leaves no time for anything else like calculating the next line , or any game/dynamic(sprites) stuff.
This is where the other pic comes in.. while the first pic is dedicated in drawing it's line , the second one calculates
what the next line will be.. once the first one is done , they switch control of the TV and the second one
starts drawing it's calculated line , while the first one is now calculating the next line that it will draw.

3. How do the two microcontrollers communicate?
The two microcontrollers use the hardware MSSP module that the pic16f877a offers, plus some signals for vertical and
horizontal syncronization . MSSP stands for Master Slave Syncronous Protocol , and it's a serial communication ( wire connections can be seen on schematics ). When the two microcontrollers run a game , they must syncronize there input
and game state. thats what happening during the little cycles of TV syncronization when there is some spare time until the
TV moves its electrone beam (CRT TVs) to the start of the frame.

You need this voltages for syncronization ( 0 - 0.3V) and drawing ( 0.3V black -> 1V white ).
I used two resistors to form a voltage divider, so depending on the combination of the voltages
the PICs give (0V and 5 V) it can achive these voltages.

And a little video demonstration
.

 

Basic Info about PAL

I used the europian PAL format. you can see a nice pic with it's basic specifications bellow

(i don't remember where i got this , so i can't link it )