Semiconductor
MSM7715
1/21
Semiconductor
MSM7715
Multi-Function Telecommunication LSI
GENERAL DESCRIPTION
The MSM7715 is a signal transmitting and receiving LSI device for applications such as
telemeters. The MSM7715 uses a no-ringing communication mode. Built-in functions includes
a 300 bps full-duplex modem complying with ITU-T V.21, a DTMF signal (PB signal) generator
and receiver, and a call progress tone (CPT) detector. The answer tone (1650 Hz) generation can
be accomplished with the built-in modem.
A meter terminal can be configured using this transmitting and receiving device along with the
meter, NCU, and controller.
FEATURES
3 V power supply. (Voltage range is 2.5 V to 3.6 V.)
Selectable modes, including DTMF signal sending mode, DTMF signal receiving mode, and
V.21 modem answer/originate mode.
For DTMF signal reception, support for normal detection mode or high-speed detection mode.
For call progress tone detection, support for rectangular wave output or detection output.
DTMF signal receiving output, which is in a 3-state mode, is able to be connected externally
with the DTMF signal sending 4-bit input.
Analog loopback test and remote digital loopback test supported.
Dedicated pins for modem sending/receiving data, carrier detection, sending request, and call
progress tone detection.
Independent external adjustment of the analog signal using the modem signal and DTMF
signal.
External adjustment of the carrier detection level.
Internal 3.579545 MHz crystal oscillation circuit.
Power-down mode
Package:
44-pin plastic QFP (QFP44-P-910-0.80-2K)
(Product name : MSM7715GS-2K)
E2A0030-16-X1
This version: Jan. 1998
Previous version: Nov. 1996
Semiconductor
MSM7715
2/21
BLOCK DIAGRAM
DT1
DT2
DT3
DT4
SP
DTTIM
CP
CPW
CD
RD
TD
RS
CLK
X2
X1
MODE1
MODE2
MODE3
ICTA
ICTB
TEN
DTG1
DTG2
DTG3
DTG4
AIN
AOUT
GAT2
GAT1
MOD
VR1
VR2
SGO
SGC
DTO
PON
V
DD
GND
Mode
Select
&
Test
FSK Modem
Carrier
Detector
CPT
Detector
DTMF
Receiver
2765 Hz
BEF
Pre-
LPF
Smooth
Voltage
Ref.
SG
DTMF
Generator
+
+
+
*
*
*
*
*
*
*
*
*
*
*
*
*
Power ON
+3 V
0 V
4 dB
Note)
DT1 to DT4 :
3-state outputs
* :
Input with
pull-up resistor
*
*
Semiconductor
MSM7715
3/21
PIN CONFIGURATION (TOP VIEW)
12
X1
44-Pin Plastic QFP
13
X2
14
NC
15
CLK
16
RD
17
CD
18
CP
19
DT1
20
DT2
21
DT3
22
DT4
44
DTG3
43
DTG2
42
DTG1
41
GND
40
VR2
39
VR1
38
DTO
37
MOD
36
GAT2
35
GAT1
34
SGC
1
DTG4
2
TEN
3
TD
4
RS
5
CPW
6
ICTA
7
ICTB
8
DTTIM
9
MODE1
10
MODE2
11
MODE3
33
NC
32
SGO
31
AIN
30
NC
29
V
DD
28
NC
27
AOUT
26
NC
25
NC
24
PON
23
SP
NC : No connect pin
Semiconductor
MSM7715
4/21
PIN DESCRIPTION
DTG4
Pin No.
I/O
Name
1
TEN
2
TD
3
RS
4
CPW
5
ICTA
6
ICTB
7
DTTIM
8
MODE1
9
MODE2
10
MODE3
11
X1
12
X2
13
CLK
15
RD
16
CD
17
CP
18
DT1
19
DT2
20
DT3
21
DT4
22
SP
23
PON
24
AOUT
27
I*
I*
I*
I*
I*
I*
I*
I*
I
O
O
O
O
O
O
O
I*
O
Description
Input for specifying the DTMF code to be sent.
Input for selecting the operation mode. See Table 1.
Outputs for the code of the received DTMF signal. In a mode other than the
DTMF receiving mode, these pins are in a high-impedance state.
Inputs for testing. Leave them open or connect them to V
DD
.
Input for controlling output of the DTMF signal. (Transmit enable)
DTG1 to DTG4 are latched at the falling edge of TEN and the DTMF signal is
output when "0" is input. See Fig. 2.
Input for data to be sent to the modem. Input the data string at a speed of 300 bps
or lower.
Input for controlling the modem sending output. (Request to send)
The sending signal is output when "0" is input.
Input for selecting the output waveform from the call progress tone detector.
When "1" is input, a rectangular wave that is synchronized with the input signal is
output from the CP.
When "0" is input, presence of detected signal is output from the CP pin. See Fig.3.
Input pin for controlling the detection timing of the DTMF receiver.
When "0" is input, the high-speed detection mode is selected.
Input and output connected to the crystal oscillator. See "Oscillation Circuit" in
the Functional Description.
3.579545 MHz clock output
Output for serial data received by the modem. It is held in the marked state
("1") when the carrier detector (CD) does not make detection.
Output for the carrier detector. "0" means detection, while "1" means
non-detection.
Output for call progress tone (CPT) detection. When the CPT is detected,
the waveform selected by the CPW pin is output. See Fig. 3.
Output for presenting the DTMF signal receiving data. "1" means that the DTMF
signal is being received. Latch DT1 to DT4 at the rising edge of SP.
See Fig. 1.
Input for controlling power-on. When "1" is input, all lines of this device enter the
power down state, and then the operation of each funciton stops and the receiver
timer is reset.
Analog signal output. The DTMF signal or modem sending signal is output.
Semiconductor
MSM7715
5/21
V
DD
Pin No.
I/O
Name
29
Description
Power supply. Supply +2.5V to 3.6V.
AIN
31
I
Input for the analog receiving signal.
SGO
32
O
Output for the signal ground voltage. The output voltage is 1/2 V
DD
.
Connect a capacitor of 0.1 mF or more between SGO and GND.
SGC
34
Pin for connecting the capacitor of the signal ground voltage generating circuit.
Connect a capacitor of 1 mF or more between SGC and GND.
GAT1
35
I
Input for the sending output level-adjusting amplifier.
GAT2
36
O
Output for the sending output level-adjusting amplifier.
MOD
37
O
Output for the sending modem signal.
DTO
38
O
Output for the DTMF signal.
VR1
39
O
Output for the reference voltage generating circuit.
The potential difference between VR1 and SGO is approximately +0.75 V.
VR2
40
I
Input for external adjustment of the modem's carrier detection level.
GND
41
Ground.
DTG1
42
I*
Inputs for specifying the DTMF code to be sent.
Data is latched at the falling edge of TEN.
DTG2
43
DTG3
44
--
--
--
Note:
Digital inputs that are pulled up internally by a high resistance.
Semiconductor
MSM7715
6/21
ABSOLUTE MAXIMUM RATINGS
Parameter
Condition
Unit
Rating
V
DD
0.3 to 7
Power Supply Voltage
Ta = 25C
With respect to GND
--
Input Voltage
Storage Temperature
0.3 to V
DD
+ 0.3
65 to +150
V
I
T
STG
Symbol
V
C
V
RECOMMENDED OPERATING CONDITIONS
ELECTRICAL CHARACTERISTICS
DC Characteristics
Notes:
*1 The following pins have an internal pull-up resistor. : DTG1 to DTG4, TEN, TD, RS,
CPW, ICTA, ICTB, DTTIM, MODE1 to MODE3, and PON
*2 RD, CD, CP, DT1 to DT4, and SP
Parameter
Min.
Unit
V
DD
Power Supply Voltage
Operating Temperature Range
Input Voltage
Condition
Symbol
Typ.
Max.
Input Clock Frequency
X1/X2 Load Capacitance
SGC Bypass Capacitance
V
DD
Bypass Capacitance
Oscillation Frequency
Frequency Deviation
Temperature
Characteristics
Equivalent Series
Resistance
Load Capacitance
T
op
V
IH
V
IL
f
CLK
C1, C2
C3
C5
--
--
--
--
--
--
--
--
Against 3.579545 MHz
--
--
--
--
At 25C 5C
At 40C to +85C
--
--
2.5
40
0.8 V
DD
0
0.1
--
--
10
--
100
50
--
--
3.0
--
--
--
--
12
1
--
--
--
--
16
3.6
+85
V
DD
0.2 V
DD
+0.1
--
--
--
--
+100
+50
90
--
V
C
V
%
pF
mF
MHz
ppm
W
pF
Crystal
3.579545
SGO Bypass Capacitance
C6
--
0.1
--
--
Parameter
Min.
Unit
I
DD1
Power Supply Current
Condition
Symbol
Typ.
Max.
Input Current
I
DD2
I
DDS
I
IH
I
IL
V
OH1
V
OL1
--
--
--
10
50
V
DD
0.1
0
3
2.4
1
--
10
--
--
6
5
20
10
10
V
DD
0.1
mA
mA
V
Modem mode
DTMF mode
Power-down
PON = "1"
PON = "0"
V
IH
= V
DD
V
IL
= 0 V
*2
*1
Output Voltage
*2
(V
DD
= 2.5 V to 3.6 V, Ta = 40C to +85C)
V
OH2
V
OL2
0.9 V
DD
0
--
--
V
DD
0.1 V
DD
CLK
C
L
10 pF
I
OH
= 100 mA
I
OL
= 100 mA
I
OH
= 100 mA
I
OL
= 100 mA
Semiconductor
MSM7715
7/21
Parameter
Min.
Unit
V
DTTL
Transmit Level
Condition
Symbol
Typ.
Max.
V
DTTH
V
DTDF
f
DDT
THD
DT
t
SDT
16.5
15.5
0
1.5
--
dBm
*1
dB
ns
Low-group tone
High-group tone
DTTIM = "1"
High-group tone/low-group tone
AOUT, R1 = R3
With respect to the nominal frequency
Harmonics/Fundamental frequency
See Fig. 2.
(V
DD
= 2.5 V to 3.6 V, Ta = 40C to +85C)
Transmit Signal Level
Relative Value
Transmit Frequency
Deviation
Transmit Signal
Distortion Rate
DTG1 to DTG4 Input Data
Setup Time
DTG1 to DTG4 Input Data
Hold Time
Receive Detect Level
Receive Reject Level
Receive Frequency
Detect Band
Receive Frequency
Reject Band
Allowable Receive Level
Difference
Allowable Receive
Noise Level ratio
Dial Tone Reject Ratio
Signal Repetition Time
Tone Time for Detect
Tone Time for No Detect
Output Delay Time
Interdigit Pause Time
Acceptable Drop Out Time
SP Delay Time
Output Trailing Edge
Delay Time
t
HDT
See Fig. 2.
V
DETDT
For each single tone
V
REJDT
For each single tone
f
DETDT
With respect to the nominal frequency
f
REJDT
With respect to the nominal frequency
V
TWIST
High-group tone/low-group tone
V
N/S
Noise (0.3 kHz to 3.4 kHz)
level/tone level
V
REJ400
380 Hz to 420 Hz
t
C1
t
C2
t
S1
t
S2
t
I1
t
I2
t
G11
t
G12
t
P1
t
P2
t
B1
t
B2
t
SP1
t
SP2
t
D1
t
D2
DTTIM = "0"
DTTIM = "1"
DTTIM = "0"
DTTIM = "1"
DTTIM = "0"
DTTIM = "1"
DTTIM = "0"
DTTIM = "1"
DTTIM = "0"
DTTIM = "1"
DTTIM = "0"
DTTIM = "1"
DTTIM = "0"
DTTIM = "1"
DTTIM = "0"
250
250
46
--
--
3.8
6
--
37
120
70
49
34
--
--
30
30
21
--
--
6
1
21
14.5
13.5
1
--
--
--
--
--
--
--
--
--
12
--
--
--
--
--
--
--
45
32
--
--
--
--
8
1.7
29
21
12.5
11.5
2
+1.5
23
--
--
10
60
1.5
--
+6
--
--
--
--
--
--
24
9
57
--
--
10
3
10
3
35
%
dB
dBm
*1
%
dB
ms
t
S
> 80 ms
t
S
> 44 ms
See Fig. 1
20
42
15
27
t
G21
DTTIM = "1"
48
30
77
t
G22
DTTIM = "0"
35
20
62
Normal
condition *2
Just after
mode change *3
AC Characteristics (DTMF)
Semiconductor
MSM7715
8/21
Parameter
Min.
Unit
V
AOM
Modem Transmit Level
Condition
Symbol
Typ.
Max.
11
dBm
(V
DD
= 2.5 V to 3.6 V, Ta = 40C to +85C)
9
7
V
DM
1.5
0
1.5
f
OM
976
980
984
f
OS
1176
1180
1184
f
AM
1646
1650
1654
f
AS
1846
1850
1854
V
AIM
48 *1
--
6
V
ON
--
44
42
V
OFF
48
46
--
V
HYS
--
2
--
t
CDD1
--
8
--
t
CDH1
20
31
40
D
BS
--
--
10
V
NR
--
--
2
Modem Receive Signal Level
Modem Transmit
Carrier Frequency
Carrier Detection (CD)
Signal Level
CD Level Hysteresis
CD Delay Time
CD Hold Time
Demodulated Data Bias
Distortion
NRTS Signal Versus
Modem Receive Signal
Allowable Level Ratio
Measured at AOUT pin, R1 = R2
Mark signal/space signal
Originate mode
Answer mode
Measured at AIN. FSK modulation signal
Answer mode : 1080 Hz
Originate mode : 1750 Hz
VR2 open at AIN pin
OFF 6 dBm
6 dBm OFF
300 bps,1 : 1 pattern
V
NRTS
/V receive modem signal
NRTS : 2765 Hz 30 Hz
Mark, TD = "1"
Space, TD = "0"
Mark, TD = "1"
Space, TD = "0"
OFFON
ONOFF
dB
Hz
dBm
dB
ms
%
dB
Signal Level Relative Value
5
14
22
--
23
--
OFF 40 dBm
40 dBm OFF
t
CDD2
t
CDH2
t
RDD
--
5
--
Receive data output Delay
Time
AIN RD
ms
t
ADD
--
3.5
--
Transmit Signal Output Deray
Time
TD AOUT
ms
Note:
*1 0 dBm = 0.775 Vrms (For all AC characteristics)
*2 "Normal condition" means that a DTMF signal appears after more than 20 ms after
setting DTMF receive mode.
*3 "Just after mode change" means that there is an input signal when the mode is
changed from DTMF transmit mode to DTMF receive mode. If there is an input
signal when power is turned on, see "DTMF mode setting procedure after power on
or after releasing power down mode".
AC Characteristics (Modem)
*1 When the carrier detector does not detect (CD="1"), RD is fixed to "1".
AC Characteristics (Call progress tone detector)
Parameter
Min.
Unit
V
DETCP
CPT Detect Level
Condition
Symbol
Typ.
Max.
40
dBm
(V
DD
= 2.5 V to 3.6 V, Ta = 40C to +85C)
--
6
CPT Non-Detect Level
CPT Detect Frequency
CPT Non-Detect Frequency
CPT Detect Delay Time
CPT Detect Hold Time
V
REJCP
f
DETCP
f
REJCP
t
DELCP
t
HOLCP
400 Hz
400 Hz
See Fig. 3.
See Fig. 3.
--
--
--
dBm
--
60
380
Hz
--
420
500
Hz
--
--
--
--
300
--
ms
20
--
--
ms
15
--
Semiconductor
MSM7715
9/21
AC Characteristics
Parameter
Min.
Unit
V
AOUT
Output Load Resistance
Condition
Symbol
Typ.
Max.
R
LX
R
LVR1
R
LAO
R
OX
R
AI
--
20
40
30
--
--
--
--
--
--
100
10
1.1
--
--
--
--
--
Resistor between VR1 and SGO
AOUT
AOUT, MOD, DTO, GAT2, VR1, SGO
GAT1, AIN
(V
DD
= 2.5 V to 3.6 V, Ta = 40C to +85C)
Output Impedance
Input Impedance
Output DC Potential
Out-of-band Output Noise
V
SG
V
DCAO
V
REF
V
S1
V
S2
V
S3
MOD, DTO, GAT2
AOUT
SGO
AOUT
Potential difference between VR1 and SGO
Measured at AOUT
4 kHz to 8 kHz
8 kHz to 12 kHz
every 4 kHz
V
DD
/20.1 V
DD
/2 V
DD
/2+0.1
--
V
DD
/2
--
0.7
0.75
0.8
--
--
45
--
--
65
--
70
60
Vp-p
kW
W
MW
V
dBm
Transmit Signal Output Level
bandwidth of
12 kHz or more
R1= 30 kW
C4 = 680 pF
Semiconductor
MSM7715
10/21
TIMING DIAGRAM
When DTMF is received
Figure 1 DTMF Receive Timing
t
S
: Tone time for detect
When the input signal duration is t
S
or more, receiving is normally done.
t
I
: Tone time for no detect
When the input signal duration is t
I
or less, this input signal is ignored and DT1 to
DT4 and SP is not output.
t
P
: Interdigit pause time
When there is no input signal for t
P
or more, DT1 to DT4 and SP are reset.
t
B
: Acceptable drop out time
DT1 to DT4 and SP are not reset even though a no-signal state for t
B
or less
(momentary no-signal) occurs during signal receiving. The t
B
is applicable while
the received signals are output. (SP="1")
t
SP
: SP delay time
Against the DT1 to DT4 output, SP is output after a delay of t
SP
. Therefore, latch DT1
to DT4 at the rising edge of SP.
t
C
: Signal repetition time
For normal receiving, set the signal repetition time to t
C
or more.
t
G1n
: Output delay time (n: 1 or 2)
Against the appearance of the input signal, DT1 to DT4 are outputs after a delay of
t
G1n
.
t
D
: Output trailing edge delay time
Against the stop of the input signal, DT1 to DT4 and SP stop outputting after a delay
of t
D
.
AIN signal
DT1 to 4
SP
t
C
t
S
t
P
t
I
t
G
t
D
t
SP
t
B
Semiconductor
MSM7715
11/21
When the DTMF tone is sent
Figure 2 DTMF Transmit Timing
When the call progress tone (CPT) is detected
TEN
DTG1
DTG2
DTG3
DTG4
DTO
t
SDT
t
HDT
941 Hz + 1447 Hz
Figure 3 Call Progress Tone Detect Timing
AIN
CP
CPW = "1"
CP
400 Hz
CPW = "0"
t
DELCP
t
HOLCP
Semiconductor
MSM7715
12/21
FUNCTIONAL DESCRIPTION
Oscillation circuit
Connect a 3.579545 MHz crystal resonator between X1 and X2. If the load capacitance of the
crystal resonator is 16 pF, connect a 12 pF capacitor between X1 and GND and between X2 and
GND.
When an external clock is used, input the external clock to X2 via a 200 pF capacitor and leave
X1 open.
Figure 6 Signal Ground
Digital input pin
The digital input pin contains a pull-up resistor. Therefore, supply the V
IH
voltage (V
DD
) to this
pin or open this pin to input "1". To input "0", supply the V
IL
voltage (GND) to this pin.
Upon power down (PON = "1"), this pull-up goes into a high-impedance state. Therefore, current
is not affected upon power down even though the V
IL
voltage remains connected to the digital
input pin.
C1
X1
C2
X2
X1
X2
3.579545 MHz
3.579545 MHz
Signal ground
Connect a capacitor of 1 mF between SGC and GND. Do not connect anything other than this
capacitor to the SGC pin.
SGO can also be used as the reference voltage for the peripheral circuit. A capacitor of 0.1 mF or
more should be connected between SGO and GND.
Figure 5
Connection of
the External Clock
Figure 4
Connection of
the Crystal Resonator
+
SG voltage
generating
circuit
To the internal
circuit
To the
peripherals
SGC
SGO
C3
+
+
C6
Semiconductor
MSM7715
13/21
Operation mode selection
By setting the MODE1 to MODE3 pins, an operation mode can be selected (see Table 1). The call
progress tone detector (CPT DET.) can be operated in the DTMF signal transmit mode and
modem mode. However, since the carrier detector is also used for the call progress tone detector,
only rectangular waveform output is available in modem mode. Set CPW = "1" when activating
the call progress tone detector in a modem mode.
Table 1 Operation Mode Table
* means active.
Note:
The carrier detecor may malfunction within 40 ms after the operating mode is changed
from the DTMF or power down mode to the modem mode.
Therefore, ignore an output signal from CD and RD during this period of time.
DTMF mode setting procedure after power-on or after releasing power-down mode
The following is a recommendable procedure to use DTMF mode after power-on or after
releasing power-down mode.
(1)
Put power-on or release power-down mode.
(2)
Set DTMF signal transmit mode. PON="0", TEN="1"
(3)
Wait more than 20 ms, V
DD
must be more than 2.5 V after this wait time.
(4-1)
In the case of DTMF receive, set DTMF signal to receive mode.
(4-2)
In the case of DTMF transmit, it is possible control transmit enable (TEN).
Modem mode setting procedure after power-on
The following is a recommendable procedure to use Modem mode after power-on.
(1)
Power on.
(2)
Set PON="1", TEN="1" and RS="1". Set mode to be used.
(3)
More than 200 ms after V
DD
becomes more than 2 V, set PON="0".
(4)
Wait more than 20 ms. V
DD
must be more than 2.5 V after this wait time.
(5)
It is possible to control transmit output. Ignore an output signal from CD and RD of
more than 40 ms which includes the wait time of term (4).
MODE
3
1
2
CPT DET.
CPW = "0"
CPW = "1"
FSK
MODEM
DTMF
GEN.
Functional Block
Operation Mode
*
0
0
0
0
1
0
0
0
1
0
1
1
1
0
0
1
1
0
1
0
1
1
1
1
DTMF
REC.
DTMF mode
Modem
mode
Normal
operation
Test
mode
DTMF signal transmit
DTMF signal receive
Originate (O)
Answer (A)
Analog loopback
(ALB)
Remote digital
loopback (RDLB)
O
A
O
A
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
Semiconductor
MSM7715
14/21
Modem signal flow
Figure 7 shows the signal flow during normal modem operation.
AIN
Receive filter
Demodulator
Transmit filter
Modulator
AOUT
RD
TD
Line
Received data
Transmitted data
Figure 7 Signal Flow in Normal Operation
The MSM7715 uses the analog loopback test (ALB) mode and remote digital loopback test
(RDLB) mode as the modem testing functions. In these test modes, the signal flow shown in
Figure 8 is used. O (originate)/A (answer) in the test mode is the expression based on the
modulator side. In ALB mode, the transmit analog signal is input to the demodulator and can
be monitored as RD. In RDLB mode, the modem is configured as the remote modem in the RDL
test mode.
Data from the other modem that requested for RDL is returned to the other modem as a result
of echo-back.
AIN
Receive filter
Demodulator
Transmit filter
Modulator
AOUT
RD
TD
Received data
Transmitted data
AIN
Receive filter
Demodulator
Transmit filter
Modulator
AOUT
RD
TD
Received data
Transmitted data
[ALB]
[RDLB]
Figure 8 Signal Flow in Test Mode
Semiconductor
MSM7715
15/21
DTMF signal code
Sixteen types of DTMF transmit signals can be set by using DTG1 to DTG4. Also, sixteen types
of DTMF receive signals can be monitored by using DT1 to DT4. Table 2 shows the DTMF signal
codes.
Table 2 DTMF Signal Codes
Low-group signal (Hz)
697
Button
DT1
DTG1
DT2
DTG2
DT3
DTG3
DT4
DTG4
770
852
941
1209
1336
1477
1633
High-group signal (Hz)
*
*
1
0
0
0
1
*
*
2
0
0
1
0
*
*
3
0
0
1
1
*
*
4
0
1
0
0
*
*
5
0
1
0
1
*
*
6
0
1
1
0
*
*
7
0
1
1
1
*
*
8
1
0
0
0
*
*
9
1
0
0
1
*
*
0
1
0
1
0
*
*
*
1
0
1
1
*
*
#
1
1
0
0
*
*
A
1
1
0
1
*
*
B
1
1
1
0
*
*
C
1
1
1
1
*
*
D
0
0
0
0
Semiconductor
MSM7715
16/21
Microcontroller interface
By externally connecting DT1 to DT4 and DTG1 to DTG4 respectively, a 4-bit bus can be
configured (Fig 9).
In DTMF signal transmit mode, DT1 to DT4 enter a high-impedance state and this 4-bit line is
used to set the DTMF code against DTG1 to DTG4. The bus data is latched at the falling edge of
TEN.
In DTMF signal receive mode, DT1 to DT4 enter an output state. The 4-bit bus line is used as the
output of the DTMF code from DT1 to DT4 to the microcontroller. Latch this bus data at the rising
edge of SP.
In modem mode, DT1 to DT4 enter a high-impedance state. This 4-bit bus line is pulled up by
the pull-up resistor in DTG1 to DTG4.
In power-down mode (PON = "1"), DT1 to DT4 enter a high-impedance state. Since the pull-up
resistors in DTG1 to DTG4 also enter a high-impedance state, potential of this 4-bit bus line
becomes unstable from the MSM7715.
Microcontroller
DTMF Generator
DTMF Receiver
DTG1
DTG2
DTG3
DTG4
DT1
DT2
DT3
DT4
Figure 9 Microcontroller Interface Example
Semiconductor
MSM7715
17/21
Setting the transmit signal level
Figure 10 Setting the Transmit Signal Level
The modem's modulated analog signal and DTMF signal are not transmitted at the same time.
The signal to be transmitted is determined by the selected operation mode. This device provides
the pins for individual setting of transmit signal levels.
V
AOM
: Level of the modem signal at the AOUT pin when R1 = R2 (dBm)
V
AODT
: Level of the DTMF signal at the AOUT pin when R1 = R3 (dBm)
When external resistors (R1, R2, R3) are changed, the signal level at AOUT is as follows:
V
AO
(modem) = 20 log (R1/R2) + V
AOM
V
AO
(DTMF) = 20 log (R1/R3) + V
AODT
However, to avoid distorted output, R1
R2 and R1
R3 are needed. In circuit design, R1 = R2
or R1 = R3 with 5% tolerance is permitted.
C4 is a component in the first order LPF for suppressing the out-of-band output noise. Select a
value C4 in such a way that cutoff frequency F
C
determined by R1 and C4 will be approximately
8 kHz.
C4 = 1/ (2p R1 F
C
)
RC-LPF
DTMF
Generator
Modulator
AOUT
GAT2
GAT1
DTO
MOD
C4
R2
R1
R3
VAO
4dB
R1, R2, R3 20 kW, R1 R2, R1 R3
+
Semiconductor
MSM7715
18/21
External adjustment of the carrier detection level
R4
R5
VR1
VR2
SG
r
1
r
2
COMP
VREF
r
1
: 300 kW, r
2
: 600 kW
R4 + R5 20 kW
12
6
11
Figure 11 External Adjustment of the Carrier Detection Level
The carrier detection level is determined by the resistance ratio between the MSM7715's internal
resistors r1 and r2, unless external resistors R4 and R5 are connected.
By connecting external resistors R4 and R5, the detection level can be adjusted. However, the
width of hysteresis cannot be changed.
Ra = R4 r
1
/(R4 + r
1
), Parallel-connected resistance of R4 and r
1
Rb = R5 r
2
/(R5 + r
2
), Parallel-connected resistance of R5 and r
2
V
ON
= 20 log (Rb/(Ra + Rb)) 40.5 (dBm)
V
OFF
= 20 log (Rb/(Ra + Rb)) 42.5 (dBm)
Caution:
r
1
and r
2
may vary in similar proportions over a 0.5 to 2.0 range, due to the lot
variation and temperature variation.
Semiconductor
MSM7715
19/21
Analog Interface
600 W : 600 W
r
4
r
3
+
R7
R6
+
+
R9
R8
+
AMP1
AMP2
+
R10
600 W
AOUT
AIN
4 dB
V
T
V
R
Line
SGO
C7
R11
R12
R13
R14
SG
C9
C8
R1560 kW
R15
Figure 12 Analog Interface Circuit Example
When R1 = R2 in the modem mode, the AOUT output level is at its maximum value of about 9
dBm. When R1 = R3 in DTMF mode, the AOUT output level is at its maximum value of 11 dBm
(sum of the low group and high group). To increase the transmit output level in the line to a high
level, use an external amplifier (AMP1).
The receive signal levels can be adjusted by the values of R13 and R14.
Clock noise of about 70 dBm will be generated from AOUT as out-of-band noise. (Clock noise
has a frequency of 27.965 kHz and its odd harmonics.) The clock noise level is nearly always
constant even if the output level of AOUT is lowered by varying the values of resistors R1 to R3
that are connected to GAT1, GAT2, DTO, and MOD. Therefore, to suppress this noise output to
the line, build a LPF at the AMP1. Note, however, that setting the cutoff frequency of the LPF
too low affects the output signal level.
Note that too large a time constant determined by the values of C9 and R15 allows the longer time
required for reaching a stable DC level, which may result in the violation of specification for the
DTMF signal receive output delay time.
Example: R15=100 kW, C9=0.022 mF.
Larger circuit-return levels of the transmit signal to the AIN pin can cause receive data errors.
If the line impedance is equal to the R10 impedance, R8=R9 can not induce the circuit-return
levels of the transmit signal to the AIN pin.
The peripheral circuits should be designed so that the circuit-return level, including variations
of the line impedance, of the transmit signal to the AIN pin is 9 dBm or less.
Semiconductor
MSM7715
20/21
APPLICATION CIRCUIT
SGC
GAT1
GAT2
MOD
DTO
VR1
VR2
GND
DTG1
DTG2
DTG3
DT4
DT3
DT2
DT1
CP
CD
RD
CLK
X2
X1
R1
C4
Microcontroller
C5
R10
R2
R3
C3
C1
C2
+
+
+
+
C6
SGO
AIN
V
DD
AOUT
PON
SP
DTG4
TEN
TD
RS
CPW
ICTA
ICTB
DTTIM
MODE1
MODE2
MODE3
R13
R14
C9
R9
R8
R6
C7
R7
C8
Positive Supply
R11
R12
Line
R15
Semiconductor
MSM7715
21/21
(Unit : mm)
PACKAGE DIMENSIONS
Notes for Mounting the Surface Mount Type Package
The SOP, QFP, TSOP, SOJ, QFJ (PLCC), SHP and BGA are surface mount type packages, which
are very susceptible to heat in reflow mounting and humidity absorbed in storage.
Therefore, before you perform reflow mounting, contact Oki's responsible sales person for the
product name, package name, pin number, package code and desired mounting conditions
(reflow method, temperature and times).
Package material
Lead frame material
Pin treatment
Solder plate thickness
Package weight (g)
Epoxy resin
42 alloy
Solder plating
5 mm or more
0.41 TYP.
QFP44-P-910-0.80-2K
Mirror finish
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