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SECTION
MITL9103-098-180-NA
the card converts these inputs to the required
Speech Path (System Junctor) Accessing
system voltages.
9.14
Each junctor switch IC (MT8804) contains
9.10
The Power Supply Card contains the fol-
four speech paths; each speech path is
lowing circuit divisions
linked t o the corresponding speech path of sub-
-
Rectifier/Filter
-
rectifies the output from
the AC power transformer, using full wave
bridges. The rectified output is filtered to
produce RMDP and -24
V
unregulated
o u t p a
Regulators
-
regulate the output o f the
rectifiers to produce the required system
voltages.
sequent junctor switches -by a system junctor.
The circuits which are connected to the junctor
switches
(6.9
line circuits, trunk circuits, tone
generators, etcl may be interconnected to ea&
other via the speech paths Such interconnections
are controlled by instructions from the CPU
throughout the progress of a call. This concept is
illustrated in Fig 9-8.
Dial Tone
C, CO Trunks
Ground StartILoop Start
9.11
Ground Stwt (refer t o Fig.
9-61:
Ground
start is a handshake method o f initiating a
CO trunk call. The local trunk circuit grounds the
RlNG lead and awaits recognition by the CO. The
CO
signals
recognition
by
grounding
the
previously floating TIP lead 40 ms after the trunk
recognizes 100 ms ground on the TIP lead, a
termmation is placed across Tip and Ring and 40
ms later the ground on the RlNG lead is removed
The CO then provides dial tone.
Loop Start (refer to Fig.
3-71:
To seize a
9.15
When the CPU is informed o f an off-hook
condition
it
interrogates its RAM to find a
free speech path which. when found, is checked
via a diagnostic circuit The tested speech path is
then connected to the extension
t h a t
went o f f -
hook (see 9.14, Speech Path Accessing).
9.16
The CPU searches for an idle Touch Tone
Receiver and Dial Tone Generator. The re-
ceiver and generator are connected, under con-
trol o f the CPU, to the same speech path
as
the
extension that went off-hook The o f f -hook ex-
tension then receives dial tone.
Dialing Internally
(From
an Extension)
loop sm
mk.
me
hunk
PIaCes a
9-17
DP
originate
an exten-
termination across TIP and RlNG The CO senses
sion and are passed over Tip
and
Ring
the CWent
'low
mrou@ the loop and siWls mat
though me line
circuit
to
speech
D e t e p
the trunk is available by providing dial tone.
tion o f the dialed digits takes place on the re-
D. Operation
Extension Going O f f -Hook
9.13
When an extension goes off-hook
loop
current is generated This current is detec-
ted by an op-amp which forms part o f the SLlC
associated with the extension The output o f the
op-amp turns on the extension LED mounted on
the Main Card and sets a signal, OFFHOOK The
OR-HOOK signal from each of the six extension
SLIC's is placed, in turn on the data bus via Main
Card circuitry, to be looked at by the CPU. The
change in state of the OFF-HOOK signal is noted
by
the CPU and the address of the off-hook
extension is written into volatile RAM.
ceiver which
has
been connected to the same
speech path A receiver is connected when an
extension originates a call or when
it
does a
switchhook flash.
Ringing an Extension
9.18
The dialing o f a valid extension number
prompts the CPU to select the line circuit
associated with the called extension (as ,deter-
mined by the programming in the non-volatile
RAM). The CPU connects the Ringing Generator to
the called extension's line circuit, whereupon the
called extension rings. The CPU connects the
Ringback Tone Generator to the same speech
path as the calling dev~ce (extension or trunk)
which, as a result. recetves ringback tone. When
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