TW2864D datasheet(19/110 Pages) RENESAS

19 / 110 page

TW2864

FN7745 Rev. 0.00

Page 19 of 110

September 28, 2012

Video Cropping

Cropping allows only subsection of a video image to be output. The active video region is determined by HDELAY,

HACTIVE, VDELAY and VACTIVE register as illustrated in Fig7.The VACTIVE signal can be programmed to indicate the

number of active lines to be displayed in a video field, and the HACTIVE signal can be programmed to indicate the

number of active pixels to be displayed in a video line. The start of the field or frame in the vertical direction is

indicated by the leading edge of VSYNC. The start of the line in the horizontal direction is indicated by the leading

edge of the HSYNC. The start of the active lines from vertical sync edge is indicated by the VDELAY register. The start

of the active pixels from the horizontal edge is indicated by the HDELAY register. The sizes and location of the active

video are determined by HDELAY, HACTIVE, VDELAY, and VACTIVE registers. These registers are 8-bit wide, the lower

8-bits is, respectively, in HDELAY_LO, HACTIVE_LO, VDELAY_LO, and VACTIVE_LO. Their upper 2-bit shares the same

The Horizontal delay register (HDELAY) determines the number of pixels delay between the leading edge of HSYNC

and the leading edge of the HACTIVE. Note that this value is referenced to the un-scaled pixel number. The Horizontal

active register (HACTIVE) determines the number of active pixels to be output or scaled after the delay from the sync

edge is met. This value is also referenced to the un-scaled pixel number. Therefore, if the scaling ratio is changed, the

active video region used for scaling remain unchanged as set by the HACTIVE register, but the valid pixels output are

equal or reduced due to down scaling. In order for the cropping to work properly, the following equation should be

satisfied.

HDELAY + HACTIVE < Total number of pixels per line.

For NTSC output at 13.5 MHz pixel rate, the total number of pixels is 858.For PAL output at 13.5 MHz rate, the total

number of pixels is 864. HACTIVE should be set to 720.

The Vertical delay register (VDELAY) determines the number of lines delay between the leading edge of the VSYNC

and the start of the active video lines. It indicates number of lines to skip at the start of a frame before asserting the

VACTIVE signal. This value is referenced to the incoming scan lines before the vertical scaling. The number of scan

lines is 525 for the 60Hz systems and 625 for the 50Hz systems. The Vertical active register (VACTIVE) determines

the number of lines to be used in the vertical scaling. Therefore, the number of scan lines output is equal or less than

the value set in this register depending on the vertical scaling ratio. In order for the vertical cropping to work properly,

the following equation should be observed.

VDELAY + VACTIVE < Total number of lines per field

TW2864D Datasheet(PDF) 19 Page - Renesas Technology Corp