1.4.3.2.
Main Equipment Block Diagram (Figure
IO)
C
FIGURE 10 MAIN EQUIPMENT BLOCK DIAGRAM
CPU Control
consists of the
micro-processor, ROM program memory, RAM working
registers, timing and control circuitry. The CPU controls all switching and system data
manipulation.
Memory
is used as working memory, to store site dependant data and to store abbreviated
dialling numbers. It is located on the ECMB cards and has a lithium battery to retain the data
when power fails.
Power Failure Switch
automatically connects exchange lines directly through to pre-assigned
powerfail stations via the powerfail connection. At the same time the powerfail bell is connected
in parallel with the powerfail station.
Exchange Line Interface
provides the d.c. loop termination of the exchange line, ring detect
circuit, audio coupling transformer, dialling relay, line surge protection and distribution for
tones and hold music.
Earth Recall Control
is used to apply PBX earth to one wire of the exchange line pair.
Dial Control
module in one case, provides the VF tones, and in the other case, provides timing
and control circuits for the loop-disconnect decadic dialling, depending on the type of
exchange lines used.
Tone and Music Source
generates all internal system, tones and synthesises hold music, it also
provides the input for background music.
Crosspoint Switch Network
is made-up of semiconductor crosspoints and is distributed over a
number of cards. This circuit which decodes the CPU order to operate the crosspoints is
located on the EDTB card. Figure 10 shows how the crosspoint switch matrix is made-up.
Intercom Control
controls the voice switching circuits for handsfree talkback.
Station Interface
provides circuits for transmission of voice and serial data between the
stations and the M.E. There is no B pair when using the
card.
Station Data Receive and Transmit
contains microprocessors which control the transmission
of new status information from the main CPU and receive data of operations initiated at each
station.
Paging Amplifier
amplifies the systems audio signals for broadcasting through external
loudspeakers.
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