Nortel Networks Circuit Card - Manual (Page 758)

Page 758 of 906 NTAK79 2.0 Mb PRI card
553-3001-211 Standard 3.00 August 2005
Card-LAN interface
A Dual Port UART handles the functions of the serial ports for the Card-LAN
serial link and the echo canceller/test port interface. The echo/test interface is
an asynchronous 4800 bps 8-bit connected to port A of the UART. The
Card-LAN interface is an asynchronous 19.2 kbps 9 bit start/stop connected
to port B of the UART.
The connection to the echo canceler/test port is available at the backplane/
MDF connector. The signals at this port conform to the EIA RS-232C
standard.
Clock controller interface
The clock controller circuitry on the NTAK79 is identical to that of the
NTAK20 clock controller.
Though several DTI/PRI packs can exist in one system, only one clock
controller may be activated. All other DTI/PRI clock controllers must be
switched off.
Clocking modes
The clock controller can operate in one of two modes:
• tracking
• non-tracking (also known as free-run)
Tracking mode
There are two stages to clock controller tracking:
• tracking a reference, and
• locked onto a reference.
When tracking a reference, the clock controller uses an algorithm to match its
frequency to the frequency of the incoming clock. When the frequencies are
very near to being matched, the clock controller is locked onto the reference.
The clock controller will make small adjustments to its own frequency until
both the incoming and system frequencies correspond.