Struggling with VSCL and timing

cbmeeks

OK, I pretty much figured out where some of these crazy numbers come in with the NTSC Template.

For example:

vsclsync                long    1<<12+269               ' NTSC sync = 4.7us

That is a convenient way of specifying the binary value of:

000000000000_00000001_000100001101

Which means we have a PIXEL CLOCK of 1 (one) and a FRAME CLOCK of 269. Pretty neat.

Now, here is where I'm stuck. How does "269" translate to 4.7us? I cannot find the correlation anywhere.

Finally, how does the 1 pixel clock apply to the "sync" colors of:

sync                    long    $8A0200                                         ' %%0 = -40 IRE, %%1 = 0 IRE, %%2 = burst

Thanks again!

kwinn

See page 216 of the propeller manual. The 269 frame clocks is how many PLLA clocks are required to shift out the 32 bits (as either 32 x 1 bit pixels for 2 color or 16 x 2 bit pixels for 4 color). How long this takes depends on the frequency of PLLA and whether 32 x 1 or 16 x 2 pixels are being output.

The waitvid command delivers the 32 bits of pixel data and the 4 color palette to the video circuitry.