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2-14
The TID-III Data Channel Module is equipped with an automatic alarm detector which provides
a front panel indication of alarm conditions should a malfunction occur.
The TID-III Data Channel Module provides five modes of operation. Modes 1 through 3 emulate
the operation of an ECH-12 (TID-II) channel. Mode 4 emulates the operation of an ECH-11 (TID-
I) channel. An automatic mode of operation (Mode 5), allows a TDM rate to be selected, and a
channel tracks this rate within the range of 200 bps to 1.044 Mbps.
Circuit Name
Each channel may be assigned a circuit name. This name is associated with the channel, and ap-
pears in configuration, status, and diagnostics displays. Status and diagnostic routines that in-
volve the channel may be invoked by circuit name as well as circuit number.
Baud Rate
A baud rate must be specified for every MEGAMUX PLUS channel (except for PCM, fixed rate
ADPCM, and fixed rate ASP voice channels, which have pre-selected rates). When a configura-
tion is activated, the TDM sends the entered baud rate to each channel; logic on the channel mod-
ule selects the proper timing signal from the MEGAMUX PLUS clock bus. The baud rate of a
data channel is determined by the equipment connected to the channel. A CVSD voice channel
baud rate is selectable; the choice is a trade-off between aggregate bandwidth consumption (a
higher baud rate consumes more aggregate bandwidth) and voice quality (the higher the channel
baud rate, the better the voice quality). 32 kHz is the most common selection for a CVSD voice
channel baud rate.
The baud rate and voice encoding scheme for the Universal Voice Card/ ADPCM channel are
also selectable and must be specified.
There are many standard baud rates available from the MEGAMUX PLUS TDM.
If a baud rate required for a channel is not available as a standard rate, General DataComm can
provide a custom-programmed Clock Generator Plus module that produces the required timing
signal. If your system has special rates available, they are displayed for selection when SPECIAL
RATES is selected from the standard rates display.
Transmit-Receive Clock
All synchronous channels require specification of the source of transmit and receive timing. The
transmit clock is the timing signal that accompanies synchronous data entering the channel; the
receive clock is the timing signal that accompanies synchronous data leaving the channel.
All timing in a MEGAMUX PLUS TDM system must be derived from one source. If synchro-
nous data entering a channel is synchronized to some clack source that is isolated from the TDM
system, the timing for that data tends to "drift" in comparison to MEGAMUX PLUS timing. This
036R660-000, Issue 10
NOTE
When a selected circuit type is different from the actual channel module in
the slot associated with a channel number, an asterisk is displayed next to
the selected circuit type. This asterisk occurs in "Modify Channel
Parameters" displays and "TDM Configuration" dis-plays for the channel.
A channel may be configured under these circumstances to allow for future
equip-ment installations. Caution must be taken, however, to avoid
activating a configuration with disagreement between entered circuit type
and installed channel mod-ules; the channel will not operate properly.
However, if a data channel module and a voice channel module are used in
a channel configuration for CVSD, the system recognizes this as a tandem
channel arrangement and does not display an asterisk.
System Overview
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