CPU Control consists of the 280 microprocessor, 48K ROM program memory, 8K RAM site dependent
data, 1.8 MHz clock, timing and control circuitry.
Dial control generates the required decadic and VF dialling pulses. The VF signal is routed through the
crosspoint switches to the required exchange line. The decadic dial data directly controls the dialling relay
in the Exchange Line Interface.
Tone generator provides the required system tones under the CPU control.
Exchange Line Interface provides the d.c. loop termination of the exchange line, ring detect circuit, audio
coupling transformer, dialling relay, grounding relay, line surge protection and distribution for tones and
hold music.
Station Data Transmit and Receive contains a microprocessor which controls the transmission of new
status information from the main CPU and receive data of operations initiated at each station.
Crosspoint Switch Matrix is made up of semiconductor crosspoints which switch on or off under CPU
control to provide connections between various parts of the system.
Station Interface provides circuits for transmission of voice and serial data between the stations and the
ME. For two-wire station interface block diagram, refer to section 1.5.4.
Internal Music generator contains a music generating circuit, a switch selecting either internal or external
Music-On-Hold source and interface and level controls for external Music-on-Hold and Background music
sources. It also contains an external page interface circuit.
Voice switches are electronic circuits used for
intercom calls.
The Clock circuit maintains a real-time clock used to update the clock display on the handsfree stations
and for the call details recorder.
1.5.3
Station Block Diagram
A
Fig
BASIC STATION BLOCK DIAGRAM
Telephone Network, transmission circuit and Handset are connected to the ME audio path by the A-pair.
An electronic transmission circuit
for the Australian network is used with identical transducers
for transmitter and receiver.
Data Transmit and Receive converts data transmitted on the B-pair into logic levels for the CPU.
Power Regulator takes power from the B-pair to supply the station circuits.
CPU Control carries out processing of data received from the main equipment to control tones and LED’s,
as well as sending station status data back to the main equipment.
Status Lamps show the status of the system facilities and are controlled by the CPU.
Station Keys are used to invoke the system facilities and the CPU constantly monitors their status.
Dial Pad is used to input
digits. The operation of the dial is monitored by the CPU and the
information is conveyed to the main equipment.
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