U3750BM Datasheet, PDF (16/20 Pages) TEMIC Semiconductors – One Chip Telephone Circuit

U3750BM
TELEFUNKEN Semiconductors
Dialer
The IC includes a dialing circuit for either pulse dialing
or dual tone multifrequency dialing. The dialer transmits
the codes decoded by the logic keyboard on the outputs
OL and MF.
Mode Selection
The choice of dialing is made by the tri-state-level on the
DC/FV Pin
FV DC = Z
FV DC
tied to pin RESET
FV DC = 0
pulse dialing in 66/33 ms
pulse dialing in 60/40 ms
DTMF dialing calibrated
When the circuit is in pulse mode, it is possible to change
over to DTMF dialing with the “ * ” key. The code “ * ” is
sent in line. The circuit returns in pulse mode after a reset
condition or after a flash pulse (see figure 14).
Dialing Codes
The dialing codes are the numeric keys 0 to 9, and the non
numeric keys A, B, C, D, *, #. All are stored in RAM. The
codes A, B, C and D can be only transmitted by the serial
bus. In pulse dialing, the code #, B, C and D have no effect
on the dialing. The code A is filtered and corresponds to
eleven pulses.
Dialing
As soon as the code is detected by the logic keyboard and
written in RAM, it can only be loaded in the dialer if the
dialer is not occupied and a pause is not generated.
Pulse Dialing
The output which provides control signals for proper
timing in pulse dialing is pin, OL. The dialling starts with
a make time (see figure 12).
Dual tone Multifrequency Dialing
The output pin, MF, provides the multifrequency signal
to transmit in line. This signal results from the sum of two
frequency pulses modulated and requires a filter to com-
pose a dual sine wave. The frequencies are chosen in a low
group and a high group. Table 3 shows the frequency
tolerance of the output tones for DTMF signalling. In
manual dialing or in redial, output tone is timed with a
fixed duration.
Table 4 Frequency tolerance of the output tones for DTMF signaling
Standard
Frequency
Hz
Low Group
697
770
852
941
High Group
1209
1336
1477
1633
Tone Output
Frequency
Hz
697.8
768.6
848.9
940.1
1210.1
1338.2
1477.3
1636.7
Tone output frequency when using a 455 kHz ceramic.
Frequency Deviation
%
Hz
+0.12
–0.18
–0.37
–0.10
+0.85
–1.42
–3.12
–0.92
+0.09
+0.17
+0.02
+0.22
+1.11
+2.23
+0.27
+3.69
16 (20)
Rev. A1: 16.07.1996