Nortel Networks 553-3001-211 manual Card-LAN interface, Clock controller interface

Page 746 of 894 NTAK79 2.0 Mb PRI card

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.

553-3001-211 Standard 2.00 September 2004