Nevion AAV-HD-XMUX - Manual (Page 16)

AAV-HD-XMUX(-T/R)/ AAV-SD-XMUX(-T/R) Rev. G
nevion.com | 16
3.2.7 Video input switching
The default mode of operation is auto-switch between the optical and electrical inputs. The
video output may be configured to either use the internal generator, or to switch off when no
video is detected on the inputs. The card will use the internal generator while it switches
between inputs until it finds a valid video signal.
There is also a manual input mode which disables the input automatic switching between
inputs. The video generator may be also 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. If the video signal is removed
however, the input will not switch even if there is a valid signal at the other input.
3.2.8 De-glitching
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 phase 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.
3.3 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, AAV-HD-XMUX, AAV-HD-DMUX, AES, D422 or D422-MG
modules.
The data input on the back panel 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.
3.3.1 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.
3.3.2 Embedding
The AAV-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, 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 that may
be transmitted 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.