Raw Screen Parameters

[Trebor]

I'm hoping one (or more) of you gurus can provide to me the following information. I researched as much as I could, and know the information is out there. I'm just not interpreting it correctly or/and cannot decipher it due to my lack of ability (Especially those relating to reading schematics):

NTSC:
Pixel Clock =
Total Horizontal Pixels Active =
Total Horizontal Pixels Blanking =
Horizontal Blank Ending Pixel =
Horizontal Blank Starting Pixel =
Total Vertical Lines Active =
Total Vertical Lines Blanking =
Vertical Blank Ending Line =
Vertical Blank Starting Line =

If the same could be provide for PAL, it would be appreciated as well.

Thank You!

[Trebor]

Does this help, anyone?

 

 

 

I know the answers are out there...

I'm just not sure how to exactly interpret what I am looking at, especially with the two sets of different numbers/data.

 

Thanks in advance to anyone who can assist.

[EricBall]

It somewhat depends upon how you are measuring. A TV engineer measures horizontal timing from the start of the hsync pulse (Maria II Screen Layout), but from a programmatic perspective you want to know how many cycles from WSYNC to first pixel (7800 timings). M2 also gives some additional details on what is going on during that HBLANK period. MARIA takes care of all of the horizontal (and vertical, unlike the 2600) sync timings.

In the end, the NTSC 7800 has a 7,159,241Hz (2x colorburst) pixel clock for 320 active pixels per line and 136 pixels of HBLANK. (160 modes are handled by displaying each pixel for 2 pixel clocks.) Note, this means a 7800 line is one pixel too long versus the NTSC spec (so the CPU clock is sync'd to the line). Most TVs should handle this, but it would have caused major problems with the "Laserdisc adapter".

For the vertical, I'd use the 7800 timings counts. Adding an extra line to your DLL (243 vs 242) will prevent MARIA from running off the end. The 192 "active" lines is more a recommendation than anything enforced by hardware. Modern TVs are able to show 240 lines, but often will stretch the picture vertically to mask off some of the top & bottom anyway. Again, from a programmatic perspective, you can either use the CTRL register to detect VBLANK, or a DLI in your last DLL active entry to set a flag which your main application watches.

[Trebor]

Thanks, Eric. As always, you are very informative and helpful. Your work and other's helped fill the gaps in for me too here, regarding not only NTSC, but PAL as well.