VSYNC transitioning high in
window
Would be seen as if VSYNC
transitioned high when HSYNC
transitioned active
Would be seen as if VSYNC
transitioned low when HSYNC
transitioned active
HSYNC
VSYNC
Transition window
Transition window
VSYNC transitioning low in
window
HSYNC
VSYNC
VSYNC transitioning twice
in window
HSYNC
VSYNC
Not Allowed
VSYNC transitioning high before window or
remaining high during window
HSYNC
VSYNC
HSYNC Line is in vertical
blanking
VSYNC transitioning low before window or
remaining low during window
HSYNC
VSYNC
HSYNC Line is in active video
Internal Modules
151
SPRUHI7A – December 2012 – Revised June 2016
Copyright © 2012–2016, Texas Instruments Incorporated
High-Definition Video Processing Subsystem (HDVPSS)
Figure 1-99. VSYNC Equivalence When Using Transition Window
Note that VSYNC skew generally only applies to input signals that have been sampled from an analog
source, as in a NTSC/PAL decoder. If the VSYNC is a VBLANK-type signal or if the sending device is
another all-digital IC such as another device or Davinci part, then the VSYNC signal does not have a skew
since VSYNC will be aligned to HSYNC. In this case, setting cfg_fid_skew_precount = ‘0’ and
cfg_fid_skew_postcount = ‘0’ defines a minimum size window which will capture the value of VSYNC on
the same cycle that HSYNC goes active.