CH1787(1998) View Datasheet(PDF) - Cermetek Microelectronics

Part Name

Description

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CH1787
(Rev.:1998)

Small Functional Modem

Cermetek Microelectronics 

DAA

The CH1787 is designed to meet North American telephone stan-

dards as set by FCC Part 68 and DOC. The telephone line inter-

face is designed to meet 1000VAC and 1500 volt peak surge

isolation, among other parameters. As such, it will meet U.S. and

Canadian requirements and other international requirements that

specify that level of isolation. The CH1787 comes with FCC Part

68 approval, a label is provided with the registration number and

ringer equivalent. This label should be prominently displayed.

As with most countries, except the U.S., Canada requires sub-

mission 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 a consultant list.

NVRAM

NVRAM can save up to two user-customized modem configura-

tions. The AT&Wn command will store the active modem con-

figuration in one of two NVRAM locations as selected by an n of 0

or 1. The AT&Yn command selects one of the stored modem

configurations to be automatically recalled and active upon a re-

set or power up. The ATZn command immediately recalls and

activates a stored configuration. See Tables 2 and 3 for storable

S-Registers and Commands.

NVRAM can save up to four telephone numbers with up to 36

digits or modifiers in each telephone number. The AT&Zn=s com-

mand will store s, the telephone number dial string. The ATDTS=n

command will cause the modem 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 number and Cermetek number.

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 Cermetek detailed command summary-

www.cermetek.com.

Serial Host Interface

The serial interface is V.24 (EIA-232-D) compatible interface. See

pin description.

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. 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 8 Ω 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 CH1787 contains a pin called Voice/Data (V/D). This 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 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.

Figure 2. Voice/Data Port Control

SLEEP MODE

To minimize the modem power consumption, the CH1787 includes

a power down feature called the Sleep Mode. When activated the

CH1787 will automatically enter the Sleep Mode after 0 to 255

seconds of inactivity. The time of inactivity is selected by the ATS24

command and 5 seconds is the default time. The modem returns

to normal operation when a ring signal is received or is upon an

input low signal on TXD. ATS24 = 255 disables the Sleep Mode

and is the default.

_____

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. In the sleep mode, power is reduced by 50% of normal

operating power.

Transmission Speed

The transmission rate of the host computer must be 300, 1200, or

2400 bps. The modem will connect at the selected speed or will

fall back to the speed set by the remote or answering modem’s

serial interface (the DTE transmission speed). That determines

the originate speed. The modem can be either originating (calling

modem) or answering (remote modem). The following table

shows the speeds:

Originate Mode

Answer Mode

300 1200 2400*

300

300 1200 1200

1200

300 1200 1200

2400

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

300 bps) 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 modem automatically adapts to the

caller’s speed on answer calls.

Cermetek Microelectronics, Inc.

The modem matches the host’s parity when it returns status mes-

sages to the host. During a data connection, however, the modem

passes parity through without interpretation or alteration.

Document No. 603-0182 Rev. D (11/98) 2

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