Fake progressive Pal

Usually PAL TV standard uses 625 scanlines (576 visibles) in order to handle 25Hz interlaced mode. 312.5 lines are shown per-frame using even/odd style. 

In '80s the home computers (and consoles) with PAL output only generate 313 lines 50 FPS progressive, and send it out at 313/313 lines PAL.

The TV's are actually eating it and is displaying a nice stable image. Normally with a real 313/312 PAL signal there would be a half-scanline "jump" between each field to fake the illusion of 576 real lines. 


Every line is 64us.

  • HalfScanline: 32us.
  • SyncLen: 4.7us.   
  • HalfSyncLen: 2.35us.
  • VblLongPulse: 32us = 27.3us with value zero (HalfScanline - SyncLen) + 4.7us (SyncLen) with value black.
  • VblShortPulse: 32us = 2.35us with value zero (HalfSyncLen) + 29,65us (HalfScanline - HalfSyncLen) with value black.


The scanlines are of different kind. 

  1. LONG-LONG: VblLongPulse + VblLongPulse (scanlines 0 and 1)
  2. LONG-SHORT: VblLongPulse + VblShortPulse (scanline 2)
  3. SHORT-SHORT: VblShortPulse + VblShortPulse (scanlines 3,4, 310,311,312)
  4. NORMAL: (scanlines from 5 to 309) 
    • 4.7us (SyncLen) with value zero
    • 5.65us (color burst) with value black or colorBurst
    • 52us for visible area with pixel data from scanline 24 to 279 and black in ranges 5-23 and 280-309
    • 1.65us frontporch with value black