Nortel Networks Video Gaming Accessories 553-3001-211 Manual De Usuario

 NTAK79 2.0 Mb PRI card

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.

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.

The clock controller can operate in one of two modes: 

•

tracking

•

non-tracking (also known as free-run)

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.