Instruction manual

FUNCTIONAL DESCRIPTION
Port Circuits
The port circuit packs listed below provide the link between trunks and external equipment and the
TDM bus. Figure 3-5 shows the equipment types that can be connected to the digital switch by the
call processing and port circuit packs.
Analog Line (TN742/TN746)
Loop Start Trunk (ZTN77)
ATL Line (ZTN79)
MET Line (TN735)
Auxiliary Trunk (TN763)
STARLAN Interface (ZTN84)
Data Line (TN726)
Tie Trunk (TN760B)
DID Trunk (TN753)
Tip Ring Line (ZTN78)
Ground Start Trunk (ZTN76)
DS1 Interface (TN767)
Circuitry Common to All Port CPs
Eight port circuits are provided on most port circuit packs. Twenty-four circuit capability is provided
on the DS1 circuit pack. The Multibutton Electronic Telephone (MET) Line, Tie Trunk, and Auxiliary
Trunk Circuit Packs each contain four port circuits. The port circuits provide an interface between
terminals/trunks and the TDM bus. The number of port circuit packs required varies according to
customer requirements and equipment configuration. Each of the System 25 port circuit packs
contain a number of common elements (see Figure 3-6) as well as the unique port circuits. The
common elements are as follows:
● Bus Buffers
The bus buffers are the digital interface between the backplane TDM bus wires (system
bus) and the on-board circuitry (data bus). They also receive and distribute clock and frame
signals.
● On-Board Microprocessor With External RAM
The on-board processor does all low-level functions, such as scanning for changes and
relay operations. In general, it carries out commands received from the Common Control
and reports status changes to it. The external RAM stores control channel information and
port-related information.
● SAKI (Sanity and Control Interface)
The SAKI is the control interface between the Common Control that sends information via
the network control circuit down the TDM buses and the on-board circuitry controlled by the
on-board microprocessor. The SAKI receives control information (down-link messages) on
the first five time slots and, as requested by the on-board microprocessor, transmits control
information (up-link messages) on these same time slots. (Continued on Page 3-13.)
November 1995
3-9