Page 758 of 906 NTAK79 2.0 Mb PRI card553-3001-211 Standard 3.00 August 2005Card-LAN interfaceA Dual Port UART handles the functions of the serial ports for the Card-LANserial link and the echo canceller/test port interface. The echo/test interface isan asynchronous 4800 bps 8-bit connected to port A of the UART. TheCard-LAN interface is an asynchronous 19.2 kbps 9 bit start/stop connectedto 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-232Cstandard.Clock controller interfaceThe clock controller circuitry on the NTAK79 is identical to that of theNTAK20 clock controller.Though several DTI/PRI packs can exist in one system, only one clockcontroller may be activated. All other DTI/PRI clock controllers must beswitched off.Clocking modesThe clock controller can operate in one of two modes:• tracking• non-tracking (also known as free-run)Tracking modeThere 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 itsfrequency to the frequency of the incoming clock. When the frequencies arevery near to being matched, the clock controller is locked onto the reference.The clock controller will make small adjustments to its own frequency untilboth the incoming and system frequencies correspond.
