ATT System 25 Maintenance Manual

SYSTEM HARDWARE
The USART interfaces the DUCKs serial data stream to the conversion
microprocessor. The USART can be programmed by the microprocessor to
operate synchronously or asynchronously. The USART also performs the
following tasks for the port circuit microprocessor:
l
l
l
lAppends start and stop bits to parallel data received from the
microprocessor in the asynchronous mode
Converts serial data received from the DUCK to parallel data
Buffers data in both directions
Detects and generates break...

SYSTEM SOFTWARE
General
The System software consists of switched services, administrative, and
maintenance software. This software runs on top of the real-time operating
system software.
Switched Services Software
The switched services software provides voice and data call processing.
This software resides in the Call Processor and Memory circuit packs
(collectively referred to as the Common Control circuitry) and in the 8-bit on-
board microprocessors located in the port and service circuits.
The...

SYSTEM SOFTWARE
Maintenance Software
The maintenance software provides automatic periodic testing of
maintenance objects within the system as well as consistency tests among
the call status tables within the system. In addition, demand testing is
initiated when the system detects a condition requiring a need for testing.
Software tables are provided for storing error records. The records can be
accessed by maintenance personnel via the SAT. A Permanent System
Alarm (a serious error) causes an alarm...

SYSTEM SOFTWARE
Real-Time Constraints
Real-time constraints are a function of the speed of the Common Control
circuitry and the traffic load. The switch is designed so that many time-
consuming and repetitious functions are performed by processors in the port
and service circuit packs, thus relieving the common control circuits.
Traffic load, defined as the sum of static and dynamic loads, is a function of
the number of features that are executed, the frequency with which they are
executed, the system...

SYSTEM SOFTWARE
Memory Circuit Pack
Administration: Provides for administration of station and system features.
This software also supports maintenance procedures related to checking
errors and diagnosing trouble.
Feature Code Modules: Includes the software that sends and receives data
to/from the Operating System as well as controls all voice and data features
supported by the system. Station Call Processing includes the processing of
messages and data associated with voice terminal on-hook/off-hook...

SYSTEM SOFTWARE
Operating System (OS): Controls all message and data flow to/from the
Memory circuit pack and the Arch Angel Driver Interface to the
microprocessors on the port circuit packs, and to RS-232C driver interfaces.
Messages destined for a particular task are queued until the associated task
can receive them. When a task has completed a particular process, the next
message is obtained from the tasks message queue. The OS provides an
interval timer that is used to time tasks. Processes that...

SYSTEM SOFTWARE
Figure 4-1. System Software Partitioning
4-6 

SYSTEM SOFTWARE
Step-By-Step Call Description
The following is a description of a call originated between two multiline voice
terminals.
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
A microprocessor on a station port circuit pack (port controller)
continually monitors associated port circuits for switchhook
status/change and button presses.
When a user goes off-hook, the port controller detects the change.
The port controller sends an off-hook up-link message along with port
identification to the Call Processor...

SYSTEM SOFTWARE
11.
12.
13.
14.
15.
16.
17.
18.
19.
20.When the DPM collects enough digits to identify an extension
number, it stops collecting digits.
Note:If the extension number dialed is invalid, the DPM sends a
down-link message to the port circuit instructing it to listen
to time slot 07 (Reorder Tone) that is then heard by the
user. Go to Step 18.
A down-link message is sent to the originating port instructing it to
listen to time slot 06 (busy) or 08 (ringing), as appropriate. Go to Step
18 for...

MAINTENANCE STRATEGY
Fault isolation is the cornerstone of the System 25 maintenance strategy.
Maintenance activity isolates faults to one (or more) repairable or replaceable
maintenance units. Equipment should be tested in the following order:
1.Terminal equipment
2.Station wiring
3.Port circuit packs (CPs)
4.Common control circuitry
5.Power supply and cabinet
6.Backplane.
The first fault isolation step attempts to reproduce the fault, whether it is
system-detected or user-reported. If a fault can be...