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Video Display Mode Selection
The image line counter (ILCOUNT) and the image pixel counter (IPCOUNT)
track the visible image within the field. ILCOUNT begins counting at the first
display image line in each field. IPCOUNT begins counting at the first dis-
played image pixel on each line. They stop counting when they reach the
image height and image width as specified in the video display field n image
size register (VDIMGSZn).
The video clock counter (VCCOUNT) counts VCLKIN transitions to determine
when to increment FPCOUNT and IPCOUNT as determined by the video
display mode. In Y/C mode, FPCOUNT and IPCOUNT increment on each
VCLKIN rising edge. In BT.656 mode, FPCOUNT and IPCOUNT increment on
every other VCLKIN rising edge. In raw mode, FPCOUNT and IPCOUNT
increment on every 1 to 16 VCLKIN cycles as programmed by the INCPIX bits
in the video display threshold register (VDTHRLD).
FPCOUNT and FLCOUNT are compared to various values to determine when
to assert and negate various control signals. The 12-bit FPCOUNT is used to
determine where to enable and disable horizontal sync and blanking informa-
tion along each scan line. The state of FPCOUNT is reflected in the VDXPOS
bits of the video display status register (VDSTAT). Figure 4–5 shows how the
horizontal blanking and horizontal synchronization signals are triggered.
(HBLNK and HSYNC are shown active high).
Figure 4–5. Horizontal Blanking and Horizontal Sync Timing
718
719 720
FPCOUNT
HBLNK
HSYNC
FPCOUNT = HBLNKSTART
The 12-bit FLCOUNT counts which scan line is being generated. The
FLCOUNT is reset to 1 after reaching the count specified in VDFRMSZ. (For
BT.656 operation, the FRMHIGHT would be set to 525 (525/60 operation) or
625 (625/50 operation).) The state of FLCOUNT is reflected in the VDYPOS
bits of VDSTAT. Figure 4–6 shows how the vertical blanking, vertical synchro-
nization, and field identification signals are triggered. (VBLNK and VSYNC are
shown active high.)
4-6
Video Display Port
735 736
FPCOUNT = HSYNCSTOP
FPCOUNT = HSYNCSTART
799 800
857
FPCOUNT = HBLNKSTOP
0
1
SPRU629
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