
Architecture
1767
SPRUH82C – April 2013 – Revised September 2016
Copyright © 2013–2016, Texas Instruments Incorporated
Video Port Interface (VPIF)
35.2.4 Video Transmit
VPIF channels 2 and 3 are used for video transmit.
Y/C Mux
For BT.656 video, luminance (Y) and chrominance (C) values are multiplexed into a single byte-stream on
one channel (either channel 2 or channel 3).
For BT.1120 video, channels 2 and 3 function as a pair without Y/C multiplexing in the following
configuration:
•
Channel 2 transmits Y data (C buffer settings for channel 2 are ignored)
•
Channel 3 transmits C data (Y buffer settings for channel 3 are ignored)
The Y/C multiplex function for BT.656 video is enabled by setting the YCMUX bit in the channel control
registers C
n
CTRL. The YCMUX bit must be the same for both channels 2 and 3.
Transmit Clocking
Each transmit channel uses a reference input clock (CLKIN
n
) and a video output clock (CLKOUT
n
). When
transmit is enabled, VPIF will generate CLKOUT
n
with the same frequency as CLKIN
n
, and video data will
be transmitted synchronously with CLKOUT
n
.
The CLKOUT
n
output signal is enabled by setting the CLKEN bit in the channel control register C
n
CTRL;
the signal can also be inverted by setting the CLKEDGE bit in the C
n
CTRL register.
When transmitting BT.1120 video data, the two transmit channels operate as a pair. To ensure that video
data is transmitted at the same time across both channels, the CLKIN
n
signals must share the same
reference clock source.
Video Pixel Enable
The PIXEL bit of the C2CTRL and C3CTRL control registers enables the transmission of video data stored
in memory. When the PIXEL bit is set, video data is transmitted normally. When the PIXEL bit is cleared,
the VPIF will transmit blank video data (Y = 10h, C = 80h). The PIXEL bit should only be set when the
associated VPIF channel is disabled, otherwise the VPIF may output corrupt data and issue an ERROR
interrupt for buffer underflow.