mt8889csr1 Zarlink Semiconductor, mt8889csr1 Datasheet - Page 7

• Manufacturer Part Number: mt8889csr1
• Description: Integrated Dtmf Transceiver With Adaptive Micro Interface
• Manufacturer: Zarlink Semiconductor

The value of t
to be recognized by the receiver. A value for C1 of 0.1 µF is recommended for most applications, leaving R1 to be
selected by the designer. Different steering arrangements may be used to select independent tone present (t
and tone absent (t
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
maintain a valid signal condition long enough to be registered. Alternatively, a relatively short t
would be appropriate for 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.
4.0
A call progress mode, using the MT8889C, can be selected allowing the detection of various tones, which identify
the progress of a telephone call on the network.
however, call progress tones can only be detected when CP mode has been selected. DTMF signals cannot be
detected if CP mode has been selected (see Table 7). Figure 8 indicates the useful detect bandwidth of the call
progress filter. Frequencies presented to the input, which are within the ‘accept’ bandwidth limits of the filter, are
hard-limited by a high gain comparator with the IRQ/CP pin serving as the output. The squarewave output obtained
from the schmitt trigger can be analyzed by a microprocessor or counter arrangement to determine the nature of
the call progress tone being detected. Frequencies which are in the ‘reject’ area will not be detected and
consequently the IRQ/CP pin will remain low.
V
ESt
St/GT
RX
b3
b2
Read
Status
Register
IRQ/CP
in
EVENTS
0
-RX
Call Progress Filter
3
REC
DP
improves talk-off performance since it reduces the probability that tones simulated by speech will
is a device parameter (see AC Electrical Characteristics) and t
t
REC
GTA
DECODED TONE # (n-1)
) guard times. This may be necessary to meet system specifications which place both accept
A
t
Figure 7 - Receiver Timing Diagram
DP
Zarlink Semiconductor Inc.
t
REC
TONE #n
MT8889C
B
The call progress tone input and DTMF input are common,
t
GTP
7
t
PStRX
t
PStb3
t
# n
ID
C
t
DA
t
GTA
TONE
#n + 1
D
REC
t
DO
is the minimum signal duration
E
TONE
#n + 1
# (n + 1)
REC
with a long t
Data Sheet
F
V
TSt
GTP
DO
)