Nevion AV-HD-XMUX - Manual (Page 17)

AV-HD-XMUX (-T/R) / AV-SD-XMUX (-T/R) Rev. L
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The video generator may be selected to override the input video picture. The input video will
decide the timing of the output video and any embedded packets will still be used by the
module. Only the picture will be overwritten.
This setting will only be restored when GYDA is present, as the generator picture may only
be switched off again with GYDA.
Upstream video switching in a router causes glitches in the digital video. The module will
remove these glitches if the switch occurs on the correct video line for the standard in use.
The input buffer is two video lines of the longest standard and starts in the middle.
Subsequent switches will be transparent if the new signal is within a line from the original
video. There will be a glitch on the output if the new video phase is outside of this range. The
buffer will be re-aligned to the middle with the new signal phase.
3.4 Data transmission
The module can de-embed and embed asynchronous data. An AES3 audio signal is used as
a carrier. Both embedded audio and normal AES3 signals may be used to carry the RS422
data. The fiber connection usually only goes one direction so any desired return path must
be created by the user with another circuit. Return data may be sent over fiber via a link
comprising of AV-HD-XMUX, D422 or D422-MG modules.
The RJ45 data input works in one of two modes:
1. UART Mode: The data is checked for correct reception according to the configuration.
The data words are packaged and sent when present.
2. Raw sampling mode: The data input is sampled at 93.75 kHz and embedded as a
data stream. No checking is performed.
3.4.1 Data latencies
The data channel has a total latency of approximately 30µs when using raw sampling.
Normal data rates of up to 9600 may be used with raw data sampling to have a low latency.
The latency is 500µs when using the normal data encoding due to the block structure of the
AES User bits.
The configuration of the data channel is always stored in the module and used regardless of
the GYDA override switch.
3.4.2 Embedding
The AV-HD-XMUX has a RS422 data input for the embedding of control data. The baud rate
and other parameters are configured with GYDA. The factory default is 115200 baud, no
parity, and one stop bit.
The data channel is encoded in the User bits in an embedded audio stereo signal assigned
with GYDA. The factory default is Audio channels 1&2 in Group 1.
The data is sampled asynchronously at a constant bit rate. The range of baud rates is from
DC to 115,200 bps. The data bytes are either encoded as packets in the transmitted data or
transmitted as an asynchronous bit stream which may also be used to transmit a DC signal
such as GPI.
3.4.3 De-embedding
The audio channel with the data signal to be de-embedded must be configured by GYDA as
there may be several data channels available.
The AV-HD-XMUX will automatically detect the data channel format when present and output
the data on the RJ45 connector. The output driver will only be active when data is output in
UART mode. The means that the output is always active when raw data is used.