Specifications

Excalibur Multirate DAP Installation and Operation
5-12
Transmit Clock
This parameter specifies the source of timing signals for the DAP's transmit clock. This
clock determines the rate at which data is transmitted across the telephone lines. The
options available for channel timing depend on the mode of operation.
• Slave - When operating over the DDS, DDS-SC, or CC64 network, the timing is
fixed. Receive (Rx) channel timing is slaved to the DDS Rx line and transmit
(Tx) channel timing is slaved to the Rx channel timing. Data is transmitted
synchronized to a clock derived from the receive line. This option is also
available in LDM mode.
• Internal - This option is available in the LADC and LDM modes. Data is
transmitted synchronized to the DAP's internal crystal.
• External - When the DAP is operating over the DDS network and the External
option is selected for timing, the external transmit clock must be synchronized
with the network clock. Only phase differences are allowed when this option is
selected. The clock signals must be frequency locked. When operating in LADC
or LDM mode and the External option is selected for channel timing, the external
transmit clock must have an accuracy of 0.01% of the selected data rate. In
LADC or LDM mode, if an external transmit clock source is selected but is not
present, the DAP automatically reverts to internal transmit clock mode.
Notes: For units equipped with the Switched 56 IDBU feature, when the service is set
for LADC or LDM, do not set the clock to External unless the external clock is frequency
locked to the Switched 56 network.
Port Receive Clock
This parameter specifies the source of timing for the port's receive clock. This clock
determines the rate at which data is transmitted from the port into the attached device.
One of two modes can be selected:
• Internal Receive Clock Mode - When this mode is selected, the Received Data
signal presented at the DTE interface is synchronized to the clock extracted from
the network. The DTE must use the receive clock provided by the DAP to
sample the data signal. This is the recommended setting for most applications.
• External Receive Clock Mode - When this mode is selected, the Received Data
signal presented by the DAP at the DTE interface is synchronized to the External
Transmit Clock signal provided by the DTE. Since the data signal received from
the network is always synchronous to the network clock, the External Transmit
Clock signal provided by the DTE must be frequency locked to the network
clock to prevent loss of data. If the External Receive Clock Mode is selected and
the External Transmit Clock signal is not present at the DTE interface, the unit
automatically switches to the Internal Receive Clock Mode.