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PIC16 driving 640 x 480 TFT screen directly


This NEC NL6448BC20-08 display has 5V TTL inputs on all signals
making it easy to interface to small and simple microcontrollers
First try: simply turn on RED, GREEN, BLUE and sync it with line and picture sync
I found out the pixel clock can be anything from 3-30MHz and it still works, ok it flickers if it is too slow.
But it works, First I tried to let the PIC generate pixel clock, but it was way too slow. By simply using the PIC clock
as pixel clock I got the speed I needed to make it not flicker, and this also keep the data change in sync with pixel clock nice and easy,
now it is only a matter of how many PIC cycles are needes to changes dots, this will give me the dot size,
ok I could divide the pixel clock and let the PIC run faster ? or simply use a Microcontroller that dont uses 4 cycles/instruction,
maybe I have to use Atmel AVR or ARM7TDMI, I will find out in next episode. stay tuned :-)


Next try: adding more wires, adding more colors, and more speed, better sync.


The cold cathode driver was salvaged from an old defect notebook computer.


Removing the PIC controller from it's socket and connecting signals from a PC was fun,
Pixel clock MUST be exactly 25.175MHz to make it fit the PC VGA standard 60 frames sec.
Lucky me I just have one crystal osc on stock that generates exactly that, strange, maybe I got it from a VGA card 10 years ago ?

AVI Video clip TFT with picture from PC
The RGB signal from a 640 x 480 PC is simply connected to 3 comparators
the output from the 3 comparators is connected to the digital hi bit of each color
now I have a homemade 1 bit ADC converter, that is why the result is so bad,
I just wanted to prove the sync and picture system is simple to interface.
The potentiometer sets the threshold voltage, see the picture change when its changed on the video.
All I need now is 3 super fast analog to digital converters with 6 bits resolution each, to make a perfect VGA screen.

Be aware that all new TFT screens uses balanced LVDS input signals not TTL like this good old one.

Made: Jan. 2006. OZ2CPU Thomas Scherrer.