CH1782A Просмотр технического описания (PDF) - Cermetek Microelectronics

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CH1782A

Family of Ultra Small Modem Modules V.22bis-2400bps

Cermetek Microelectronics 

Cermetek Microelectronics, Inc.

submitting the design to a test house or consultant.

Call Cermetek for assistance.

SUPPORT FEATURES

AT Command Set. A 40-character command line is

supported. The command line starts with AT and

may contain standard or enhanced commands. The

commands are compatible with EIA Document

TR302.2/88-08006.

Serial Host Interface. The serial interface is a V.24

(EIA-232) compatible interface. Ten Bits total: 1 start

bit, 1 stop bit, and eight data bits which can be either

eight bits with no parity or seven odd or even with

parity. The start bit is LOW going. RXD and TXD

data is non-inverted. See pin description in Table 2.

Speaker Interface. The SPK output reflects the

receiver analog input and provides a signal that can

be used to monitor call progress. The SPK signal can

drive a 300 Ω load directly. Typically, the SPK signal

is input into an audio power amplifier and the

amplifier, in turn, drives the speaker coil. The

speaker is activated with the ATMn command. The

speaker volume is adjusted using the ATLn

command, where n is 0,1,2,or 3. Increasing numbers

correspond to higher volume. Figure 5 indicates one

method of driving an external 8 Ω speaker.

Phone Control. Cermetek ’s CH1782A contains a pin

called Voice or Data (V/D). The V/D pin toggles high

when the modem goes off hook. This pin can be used

CH1782A Family of Ultra Small Modem Modules V.22bis-2400bps

to activate a relay which can switch a telephone on or

off the Tip and Ring incoming PSTN lines. This

feature allows any telephone associated with the

CH1782A to be disconnected when a data call is in

progress, thereby preventing the data from being

disturbed by an inadvertent telephone pick-up. See

Figure 2.

Speed and Parity Selection. Prior to call initiation,

the host controller trains the modem to the host

speed (2400,1200 or 300bps) and parity (odd, even,

mark, space, or none) via a host-initiated training

sequence. This training also sets the speed of the

data for originate calls. The CH1782A will

automatically adjust to the originator’s speed when

answering calls.

The CH1782A matches the host’s parity when it

returns status messages to the host. During a data

connection, however, the modem passes parity

through without interpretation or alteration.

Sleep Mode. To minimize power consumption, the

CH1782A includes a power down feature called

Sleep Mode. When activated, the CH1782A will

automatically enter Sleep Mode after 0 to 254

seconds of inactivity. The inactivity delay is selected

using the ATS24 command. The CH1782A is

delivered from the factory with a 5 second inactivity

delay enabled (i.e., ATS24=5). The CH1782A

returns to normal operation when a ring signal is

received or upon an input low signal on the TXD pin.

ATS24=255 disables the Sleep Mode and is the

default if no value is set in register S24.

2

1

CH1782A

+5V

12

V/D

IN914

10K

RING RJ-11 OPTIONAL

TIP Jack PHONE

TIP

RING

RJ-11 TELEPHONE

Jack LINE

V/D pin is used to create a separate port for telephone connection sharing of the tip and ring

lines. V/D is TTL compatible (IOL = 1.6mA, VOL = 0.4V) and is active during data connection

thereby isolating the telephone from the tip and ring lines. (Note: the relay chosen must meet

the appropriate regulatory agency requirements).

Figure 2. Use of V/D pin to ensure that a shared PSTN line does not inadvertently disturb

an active data call.

2002 Cermetek Microelectronics, Inc.

Page 2

Document No. 607-0009 Revision C (01/03)

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