NI Digital System Development Board User Manual | © National Instruments | 33
Figure 13. VGA Display Controller Block Diagram
HDMI Source/Sink Port
An input and output-capable HDMI Port connects to the programmable logic pins. Over this
connector an HDMI or DVI-compatible video stream can be driven in or out of the DSDB.
Encoding or decoding the HDMI/DVI video stream needs to be implemented in logic, as well as
auxiliary functions, like DDC or CEC. Depending on the actual design, it can take the Source
role driving a monitor/TV display, or behave as a Sink accepting a video stream from any
HDMI/DVI Source, like a laptop or smartphone.
On-board auxiliary buffers and electronic switches control the direction of signals that differ
between Source and Sink. These signals are summarized Table 14.
The CEC function is bidirectional by definition, so it is treated the same no matter what role the
port takes. If the CEC function is not used, declare it as input and constrain it to the correct PL
pin to leave other devices on the CEC bus unaffected.
When operating as Sink, the DDC function is required to be implemented so that a connected
Source can read out important characteristics of the device. This can be done by emulating an
I2C-capable EEPROM in programmable logic. Likewise, in Source mode DDC can be used to
find out the capabilities of the connected display.
The HDMI/DVI protocol uses TMDS (Transition-minimized differential signaling) as I/O
standard. It is supported on Zynq by the I/O buffers on the programmable logic side. 50
external parallel termination resistors are provided on-board. HDMI specifications only require
terminations on the Sink side, but optional Source-side terminations reduce reflections, resulting
in improved signal quality. Do not connect powered HDMI/DVI devices to an unpowered
Table 14. HDMI Signal Direction in Source and Sink Roles
Signal Role Description
Directio
n (Zynq
POW)
How to Control
HPD Source Hot-plug detect; signals the
presence of a Sink to a
Source
Input HDMI_OUT_EN = 1
Sink Output HDMI_OUT_EN = 0
5V0 Source Auxiliary power for Sink Output HDMI_OUT_EN = 1
Sink Input HDMI_OUT_EN = 0
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