MT88L89AC MITEL [Mitel Networks Corporation], MT88L89AC Datasheet - Page 6

• Manufacturer Part Number: MT88L89AC
• Description: 3V Integrated DTMFTransceiver with Adaptive Micro Interface
• Manufacturer: MITEL [Mitel Networks Corporation]

MT88L89
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
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.
DTMF Generator
The DTMF transmitter employed in the MT88L89 is
capable of generating all sixteen standard DTMF
tone pairs with low distortion and high accuracy. All
frequencies are derived from an external 3.579545
MHz crystal. The sinusoidal waveforms for the
individual tones are digitally synthesized using row
and column programmable dividers and switched
capacitor D/A converters. The row and column tones
are mixed and filtered providing a DTMF signal with
low total harmonic distortion and high accuracy. To
specify a DTMF signal, data conforming to the
encoding format shown in Table 1 must be written to
4-130
EXPLANATION OF EVENTS
A)
B)
C)
D)
E)
F)
EXPLANATION OF SYMBOLS
V
ESt
St/GT
RX
b3
b2
IRQ/CP
t
t
t
t
t
t
t
t
REC
REC
ID
DO
DP
DA
GTP
GTA
in
microprocessor
0
-RX
3
RETAINED UNTIL NEXT VALID TONE PAIR.
RETAINED UNTIL NEXT VALID TONE PAIR.
REQUIRED GUARD TIME THUS CONSTITUTING A VALID SIGNAL. ACTIVE LOW FOR THE DURATION OF A
VALID DTMF SIGNAL.
REGISTER IS READ.
CLEARED AFTER THE STATUS REGISTER IS READ.
TONE BURSTS DETECTED, TONE DURATION INVALID, RX DATA REGISTER NOT UPDATED.
TONE #n DETECTED, TONE DURATION VALID, TONE DECODED AND LATCHED IN RX DATA REGISTER.
END OF TONE #n DETECTED, TONE ABSENT DURATION VALID, INFORMATION IN RX DATA REGISTER
TONE #n+1 DETECTED, TONE DURATION VALID, TONE DECODED AND LATCHED IN RX DATA REGISTER.
ACCEPTABLE DROPOUT OF TONE #n+1, TONE ABSENT DURATION INVALID, DATA REMAINS UNCHANGED.
END OF TONE #n+1 DETECTED, TONE ABSENT DURATION VALID, INFORMATION IN RX DATA REGISTER
DTMF COMPOSITE INPUT SIGNAL.
EARLY STEERING OUTPUT. INDICATES DETECTION OF VALID TONE FREQUENCIES.
STEERING INPUT/GUARD TIME OUTPUT. DRIVES EXTERNAL RC TIMING CIRCUIT.
4-BIT DECODED DATA IN RECEIVE DATA REGISTER
DELAYED STEERING. INDICATES THAT VALID FREQUENCIES HAVE BEEN PRESENT/ABSENT FOR THE
INDICATES THAT VALID DATA IS IN THE RECEIVE DATA REGISTER. THE BIT IS CLEARED AFTER THE STATUS
INTERRUPT IS ACTIVE INDICATING THAT NEW DATA IS IN THE RX DATA REGISTER. THE INTERRUPT IS
MAXIMUM DTMF SIGNAL DURATION NOT DETECTED AS VALID.
MINIMUM DTMF SIGNAL DURATION REQUIRED FOR VALID RECOGNITION.
MINIMUM TIME BETWEEN VALID SEQUENTIAL DTMF SIGNALS.
MAXIMUM ALLOWABLE DROPOUT DURING VALID DTMF SIGNAL.
TIME TO DETECT VALID FREQUENCIES PRESENT.
TIME TO DETECT VALID FREQUENCIES ABSENT.
GUARD TIME, TONE PRESENT.
GUARD TIME, TONE ABSENT.
or
counter
arrangement
Figure 9 - Description of Timing Events
to
the transmit Data Register.
same as the receiver output code. The individual
tones which are generated (f
referred to as Low Group and High Group tones. As
seen from the table, the low group frequencies are
697, 770, 852 and 941 Hz. The high group
frequencies are 1209, 1336, 1477 and 1633 Hz.
Typically, the high group to low group amplitude ratio
(twist) is 2 dB to com-pensate for high group
attenuation on long loops.
LEVEL
(dBm)
AAAA
AAAA
AAAA
AAAA
AAAA
AAAA
AAAA
AAAA
-25
AA
AA
AA AA
Figure 8 - Call Progress Response
0
= Reject
= May Accept
= Accept
250
FREQUENCY (Hz)
Advance Information
AAAA
AAAA
AAAA
AAAA
AAAA
AAAA
AAAA
AAAA
AAAA
AAAA
Note that this is the
LOW
AAAA
AAAA
AAAA
AAAA
AAAA
500
A
A A
A A
and f
HIGH
750
) are