CH1782A 데이터 시트보기 (PDF) - Cermetek Microelectronics
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CH1782A Datasheet PDF : 19 Pages
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Cermetek Microelectronics, Inc.
A SLEEP output signal is available to control power to
external devices. In Figure 6, a FET controlled by the
SLEEP signal turns of the external speaker amplifier
when the CH1782A enters Sleep Mode. In Sleep
Mode, power is reduced to approximately 50% of
normal operating power.
Guard Tone. A guard tone of 550 Hz or 1800 Hz can
be generated at 6 dB or 9 dB below the transmit level,
respectively, by using the &Gn command. Refer to
“Cermetek AT Commands and S-Registers reference
Guide” or the Cermetek web site at
http://www.cermetek.com.
CH1782A Family of Ultra Small Modem Modules V.22bis-2400bps
NOTE
A 2400-baud connection rate will only result if both
modems are initially set at 2400 baud.
Table 1. Connection Rates.
Answering
Modem Initial
Trained Rate
Connection Rate Resulting
When Calling Modem Initial
Rate Is:
300
1200
2400
300
300
1200
1200
1200
300
1200
1200
2400
300
1200
2400
Answer Tone. A CCITT (2100 Hz) or Bell (2225Hz)
answer tone is generated depending on the selected
configuration. Refer to “Cermetek AT commands and
S-Registers Reference Guide” or the Cermetek web
site at http://www.cermetek.com.
Data Encoding. The data encoding conforms to
CCITT recommendations V.22bis or V.22, or
Bell212A, or 103, depending on the selected
configuration. Refer to “Cermetek AT commands and
S-Register Reference Guide” or the Cermetek web
site at http://www.cermetek.com.
Ring Indicator (RI). The RI pin follows the frequency
of the ring signal and toggles low when the CH1782A
detects an incoming call. The ring signal is typically
20 to 30 Hz and is on for 2 seconds and off for 4
seconds. Although not TTL compliant, the RI pin can,
nonetheless, be utilized to activate external circuitry
including the external RST pin.
When using the RI pin, it is recommended that a
Schmitt Trigger or the Isolated Envelope Detect
Circuit in Figures 3 or 5 be placed between the RI pin
and the external load.
Line Equalization. Transmitter and receiver digital
filters compensate for delay and amplitude distortion
during operation on nominal phone lines. In addition,
automatic adaptive equalization in the receiver
minimizes the effects of inter symbol interference.
Transmission Speed. In normal operation, the
originating modem initiates the call and attempts to
connect to the answering modem at a speed
established by the originating modem’s controller prior
to call initiation. This is referred to as the Initial
Trained Rate. Upon receiving the call, the answering
modem will attempt to connect to the originating
modem at its Initial Trained Rate. If these two rates
are identical, the connection is made. If the speeds
differ, the answering modem must adjust its rate or
terminate the call. Table 1 indicates the connection
rate that will result when the calling modem’s Initial
Trained Rate and the answering modem’s Initial
Trained Rate are different.
Power Supply. The CH1782A modem module is a
complex set of sub-systems. During the course of
normal operation the CH1782A decodes analog
signals from the telephone line that are in the millivolt
range. Steps must be taken by the user to guarantee
that power supply noise on all supply lines, including
ground, does not exceed 50 mV peak to peak. Any
frequency between 20 kHz and 150 kHz must be less
than 500 micro volts peak. If necessary, use
dedicated power and ground planes. Failure to
provide such operating conditions could cause the
CH1782A to malfunction or to function erratically.
The CH1782A requires a single +5V ±5% supply. It
is recommended that by-pass capacitors be placed
on the power supply as close to the modem’s supply
input as practical. It’s recommended a 10 µF
Tantalum capacitor in parallel with a 0.01 µF ceramic
capacitor be used.
MODEM CONTROL
The CH1782A modem may be controlled by sending
serial ASCII command sequences. The commands are
sent to the modem serially on TXD. After execution of
the command, the modem returns a serial status
message on RXD, to indicate the completion status of
the command.
INITIALIZING THE MODEM
Before commands may be sent to the CH1782A, the
CH1782A must be initialized. Initialization is a two
step activity consisting of:
1. Hard Reset. This is accomplished by applying a
hardware reset pulse to pin RST or by switching
the power off and then back on.
2. Initial modem training. The CH1782A must be
trained to the host’s speed (2400, 1200, 300bps)
and parity (odd, even, mark, space or none).
2002 Cermetek Microelectronics, Inc.
Page 3
Document No. 607-0009 Revision C (01/03)
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