View Full Version : pal / vga settings

09-05-2007, 11:00 PM
Hi propellers,

Me and my friend recently developed a propeller board based on the development kit schematics. It works very good !
I have some questions on the video mode as all the samples in the library are written for NTCS mode. If I change the mode to PAL like %0001 the screen is flickering while with NTCS it's stabel. (my samsung lcd supports PAL/NTCS/SECAM cause i'm in Europe). Note that if I turn on interlace like %00011 for the mode it's even worse for both modes. I run the terminal example.

Is it sufficient to change only the mode field for PAL/NTCS or are some other fields also important to change (broadcast,..)?

I tried also some examples of VGA modes. These are working fine on my LCD monitor but if I run eg. the example of 1024/768 pixels on my samsung lcd tv with PC input the screen isn't show up at all. I think there are some more parameters to modify. The spec of my tv for 1024/768 is Hor F 60.023kHZ Ver F 75.029 HZ and pixel CLK F 78.750Mhz in a Sync polarity of H/V +/+.

Is there somewhere a document that descibes how to fulfill these frequencies to a screen ?


I use a 5MHz crystal

Keep up this great chip development !

Thanks in advance

09-06-2007, 01:10 AM
There are two problems with PAL
(1) The 5 or 10 Mhz crystal cannot generate a color clock close enough to the PAL 4.433xxx MHz, so most monitors show some moving moiree. One can try a PAL crystal rather than a 5MHz to improve this.
(2) Most monitors have 240 lines which is fine for NTSC with 480 lines. PAL has 525 which gives many interferences on a 240 lines monitor.

09-06-2007, 01:20 AM
Thanks for your tip of the crystal !

But I was planning to change the crystal to osc of 80MHz. Is that a good idea than ?

09-06-2007, 01:54 AM
No. But you can try to experiment with something a little bit above 5 Mhz. Crystals are quite cheap. It's just a matter of interference... And dont forget to state the exact value as _xinfreq

09-06-2007, 06:42 AM
You can also set the parameter hx to 12 or 13 in PAL mode, this makes the screen bigger.
An other way to reduce the flickering is to choose other colors, flickering depends much of the color combinations.


09-06-2007, 07:11 AM
I changed "lpal = 4560" in the tv driver and there's much less flicker (especially on the white color). But I did this on a try and error base, so it probably only works this way on my tv...

09-07-2007, 12:41 AM
Its so to speak a "mathematical" problem: You can come closer to a specific value by changing the counter or denominator in a devision, but not close enough with a 5 or 10 MHz crystal

09-07-2007, 02:02 AM
The maximum crystal is 8MHz ? I think I red that somewhere in de spec.
from 4-8M

09-07-2007, 04:36 AM
Hydra and the (not so popular) SpinStamp use 10 MHz; this is marginal but to my knowledge this has never failed (PLLx8 of course!)