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System Overview
The circuit type may be one of the following choices. Each selection is discussed below.
Revision Level
A1XX
T-Enc
Sync
Isoc
Async
CVSD
PCM
ADPCM
ASP
PCM-T
Undef (Undefined)
An undefined channel has no configuration, and is considered inactive by the TDM. A channel is
only undefined when the channel has never been configured, or has been placed in an undefined
state by an operator.
Sync (Synchronous)
Sync is selected when the channel is connected to equipment passing synchronous data. In syn-
chronous data transmis-sion, a timing signal accompanies the data; the timing signal is used to
precisely track the data.
Synchronous data transmission is often used for higher-speed communications, because less er-
rors occur in the transmis-sion. In a TDM system, all timing must ultimately be derived from a
single source; for that reason, sources of transmit and receive clock signals must be specified for
each synchronous channel.
Async (Asynchronous)
Async is selected when the channel is connected to equipment passing asynchronous data. Asyn-
chronous data is transmitted as characters; each character is represented .by five, six, seven, or
eight data bits, with the beginning of each character marked by a start bit, and the end of each
character marked by a stop bit. Since there are several different asynchronous character formats,
the specific format used by the channel device must be specified as a channel parameter.
Isoc (Isochronous)
Isoc is selected when the channel is connected to equipment passing isochronous data. Isochro-
nous data has neither separate timing signals nor start/stop bits; the bit transitions in the data
stream are so precisely timed that the Data II, III< IV or UDC Channel module can derive a timing
signal from the data. However, because the timing of the isochronous data is not locked to
MEGAMUX PLUS timing, there is a possibility of data errors if there is significant "drift" (dif-
ferences in the exact frequency) of the two timing systems.
Revision Level
Revision Level
2.XX
3.XX
T-Enc
--
Sync
T-Enc
Isoc
Sync
Async
Isoc
CVSD
Async
PCM
CVSD
ADPCM
PCM
CADM
ADPCM
PCM-T
TOR
U-ADPCM
ASP
Revision Level
4.XX
--
T-Enc
Sync
Isoc
Async
CVSD
PCM
CADM
ADPCM
PCM-T
TOR
U-ADPCM
ASP
TID-III
036R660-000, Issue 10
2-11
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