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Watson-TDM-Manual-W.doc
Version 2.0-01
3.4.5
Watson TDM
Operating Manual
Clock Direction
For V.35 and V.36 interface types, the clock direction can be configured by the
user. If codirectional, Transmit Data 103 is sampled with Transmit Clock 113. If
contradirectional, Transmit Data 103 is sampled with Transmit Clock 114. It is
recommended to use codirectional transmit timing whenever possible, in particular for bitrates > 32 x 64 kbit/s.
3.4.6
Clock Polarity
In X.21 mode the sampling instant for the incoming data stream on circuit T of the
user interface (UIF) can be switched to the rising or falling slope of the contradirectional clock circuit S.
Data transitions of the received data on UIF circuit R are not influenced by this
setting.
By default circuit T is sampled on rising edge of clock S. The data transitions on
T and R occur at the OFF to ON transition of S (according X.24 standard). The
ON to OFF transition of circuit S nominally indicates the center of each signal
element, in this case on circuit R.
When Clock Polarity is set to "inverted", circuit T is sampled with the falling slope
of S. The incoming data at X.21 circuit T will be sampled at the OFF to ON transition of S.
3.4.7
Byte Timing
In the X.21 mode, the byte timing circuit B according to X.24 can be activated
(Monitor command BYTETIMING) As the circuits B (byte timing) and X (codirectional transmit clock) share the same pins on the 15-pin ISO 4903 connector, special cables have to be used in this case.
3.4.8
Note:
Multiservice / nx64 Clock Modes
For V.35 and V.36, the receive and transmit clocks are independent. The receive
clock is always the recovered remote clock. The clock mode configuration only
applies to the transmit clock.
The modem is a data communications equipment (DCE). Therefore the transmit
clock is directed towards the modem, the receive clock is directed towards the
data terminal equipment (DTE).
For X.21, there is only one clock (circuit S) to receive and transmit. The clock
mode determines the source of that single clock; however, in the co-directional
nx64 Port clock mode, X is used as a co-directional transmit clock and S is used
only as receive clock.
The following clock modes are supported:
•
nx64 Port: The transmit clock is the co-directional clock coming from the
equipment connected to the nx64 port (circuit 113, X).
•
E1 Port: The transmit clock is generated based on the transmit clock used at
the E1 port. It is available at the contra-directional transmit clock output (cir-
Revision: 2008-02-07
3-17