MT8885 Mitel Networks Corporation, MT8885 Datasheet - Page 5

• Manufacturer Part Number: MT8885
• Description: Integrated DTMFTransceiver with Power Down & Adaptive Micro Interface
• Manufacturer: Mitel Networks Corporation

Advance Information
signal duration to be recognized by the receiver. A
value for C1 of 0.1 µF is recommended for most
V
St/GT
ESt
V
St/GT
ESt
V
ESt
St/GT
RX
b3
b2
Read
Status
Register
IRQ/CP
DD
DD
in
EVENTS
0
-RX
3
Figure 6 - Guard Time Adjustment
R1
R1
t
REC
DECODED TONE # (n-1)
t
t
GTP
GTP
R2
a) decreasing tGTP; (tGTP < tGTA)
b) decreasing tGTA; (tGTP > tGTA)
R2
C1
C1
= (R
= (R1C1) In [V
A
t
t
GTA
GTA
P
C1) In [V
R
R
P
P
= (R1C1) In (V
= (R
= (R1R2) / (R1 + R2)
= (R1R2) / (R1 + R2)
p
C1) In (V
DD
DD
t
DP
Figure 7 - Receiver Timing Diagram
/ (V
/ (V
DD
DD
DD
DD
-V
-V
/V
/V
t
REC
TSt
TSt
TSt
TSt
TONE #n
)]
)]
)
)
B
t
GTP
t
PStRX
applications, leaving R1 to be selected by the
designer. Different steering arrangements may be
used to select independent tone present (t
tone absent (t
necessary to meet system specifications which place
both accept and reject limits on tone duration and
interdigital pause. Guard time adjustment also allows
the designer to tailor system parameters such as talk
off and noise immunity.
Increasing t
it reduces the probability that tones simulated by
speech will maintain a valid signal condition long
enough to be registered. Alternatively, a relatively
short t
extremely noisy environments where fast acquisition
time and immunity to tone drop-outs are required.
Design information for guard time adjustment is
shown in Figure 6. The receiver timing is shown in
Figure 7 with a description of the events in Figure 9.
Call Progress Filter
A call progress mode, using the MT8885, can be
selected allowing the detection of various tones,
which identify the progress of a telephone call on the
network.
input are common, however, call progress tones can
only be detected when CP mode has been selected.
t
PStb3
t
# n
ID
C
t
REC
DA
t
GTA
with a long t
TONE
#n + 1
The call progress tone input and DTMF
REC
D
GTA
improves talk-off performance since
) guard times. This may be
t
DO
E
DO
TONE
#n + 1
# (n + 1)
would be appropriate for
MT8885
F
GTP
V
) and
TSt
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