CH1787 데이터 시트보기 (PDF) - Cermetek Microelectronics

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CH1787

Small Footprint Hardware Controllable 2400bps Modem

Cermetek Microelectronics 

Cermetek Microelectronics, Inc.

countries (except the U.S.), Canada requires

submission of the product containing the CH1787 for

DOC approval. This can be done by submitting the

design to a test house or consultant. Call Cermetek for

assistance.

NVRAM. NVRAM can save a maximum of four

telephone numbers with up to 36 digits or modifiers in

each. The AT&Zn=s command will store s, the

telephone number dial string. The ATDTS=n command

will cause the CH1787 to dial one of the four stored

telephone numbers. The NVRAM storage location for

the four telephone numbers is selected by an n of 0, 1,

2, or 3. Location 1 is used for the ORA stored numbers

and Cermetek number. The AT&Wn command will

store the active configuration in one of two NVRAM

locations as selected by an n of 0 or 1. The AT&Yn

command selects one of the stored configurations to be

automatically recalled and made active upon reset or

power up. The ATZn command immediately recalls

and activates a stored configuration. See Table 2 and

3 for storable S-Registers and Commands.

CH1787 Small Footprint Hardware Controllable 2400bps Modem

CH1787 will automatically enter Sleep Mode after a

user specified period of inactivity. The inactivity

counter increments in whole seconds and is selected

by the ATS24 command. The default is 0 seconds.

The modem returns to normal operation when a ring

signal is received or upon an input low signal on TXD.

ATS24 = 255 disables Sleep Mode.

SUPPORTED FEATURES

AT Command Set. A 40-character command line is

supported. The command line starts with AT and may

contain standard or enhanced commands. See the

Cermetek website at http://www.cermetek.com for

publication AT Commands and S-Registers.

Serial Host Interface. The serial interface is V.24

(EIA-232-D) compatible. See pin description in Table

1.

Speaker Interface. The SPK output reflects the

receiver analog input and provides a signal that can be

used to monitor call progress. Although the SPK signal

can drive a 300Ω load directly, the SPK signal is usually

input to an audio power amplifier and the amplifier

drives a speaker coil. Figure 5 shows how to drive an

8Ω speaker.

The speaker can be turned on and off with the ATMn

command. The speaker volume can be adjusted by the

ATLn command, where n is 0, 1, 2 or 3.

Phone Control. The Voice/Data (V/D) pin toggles high

when the modem goes off hook and can be used to

activate a relay which can switch a telephone on or off

the TIP and RING Telco lines. This feature allows the

telephone to be disconnected when a data call is in

progress, preventing the data from being disturbed by

an inadvertent telephone pick-up. See Figure 2.

SLEEP MODE

Sleep Mode is a power down feature designed to

minimize power consumption. When activated, the

Figure 2. Voice/Data Port Control.

A SLEEP output signal is available to control power to

external devices. In Figure 5, a FET controlled by the

SLEEP signal turns off the external speaker amplifier

when the modem enters the Sleep Mode. Sleep Mode

reduces power consumption by approximately 50%.

Transmission Speed. The CH1787 can be either

originating (calling modem) or answering (remote

modem).The transmission rate of the host computer

must be 300, 1200, or 2400bps. The CH1787 will

connect at the selected speed or will fall back to the

speed set by the remote or answering modem (the DTE

transmission speed). The following table indicates the

speeds:

Originate

Speed

300

1200

2400

Connect Speed Based on Answer

Speed of:

300

1200

2400*

300

300

300

300

1200

1200

300

1200

2400

*Pin activated operation at 2400bps only. Other

speeds may be used with AT Command operation.

Speed and Parity Selection. Before a call, the

modem adjusts to the host speed (2400, 1200, or

300bps) and parity (odd, even, mark, space, or none)

via a host-initiated training sequence. This also selects

the speed of the data for originate calls. The CH1787

automatically adapts to the caller’s speed on answer

calls.

2002 Cermetek Microelectronics, Inc.

Page 2

Document No. 607-0002 Revision B (03/02)

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