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CH1787

Small Footprint Hardware Controllable 2400bps Modem

Cermetek Microelectronics 

CH1787

Small Footprint Hardware Controllable 2400bps Modem

INTRODUCTION

The CH1787 is a small footprint, full function 2400bps,

V.22bis asynchronous modem designed to be used in

applications where there is little or no external controller

intelligence to command the modem. The CH1787

allows the user to operate the modem via hardware

resources only, not requiring AT command execution

for basic operation. For those applications where an

external controller is available, the CH1787 operates

like a standard AT Command driven modem.

The CH1787 is ideal for use as a remote modem in

applications such as alarm products and in industrial

controllers. The CH1787 will dial a pre-stored

telephone number under pin activation control to make

a connection with another modem. The CH1787 can

also answer incoming calls (either automatically or

manually) using the ANS pin. A call is terminated by

activating the HNG pin.

GENERAL DESCRIPTION OF FUNCTIONAL

BLOCKS

Figure 1 contains a functional block diagram of the

CH1787. The CH1787 is comprised of a

modulator/demodulator, controller, an FCC Part 68

approved telephone interface Data Access

Arrangement (DAA) and NVRAM.

Modulation/Demodulation and Control. This

functional Block is comprised of a monolithic modem

integrated circuit, with built-in facilities to accommodate

integrated AT command control and resident interfaces

for general communication and routing to the DAA.

Controller. The controller is a programmed

microprocessor that provides commands to the modem

in response to external pin activation. The following

pins are controlled by the microprocessor and are

described in detail in Table 1. These pins are

operational when the modem is in use at 2400bps only.

ANS

ORG

ORA

HNG

AAR

TST

Manual Answer Pin Input – Answer mode –

Places modem in answer mode

Manual Originate Pin Input – Originate

mode – Places modem in originate mode

Automatic Dial Pin Input – Dials one of two

pre-stored numbers based on TST

Forces CH1787 to disconnect

Enables Auto Answer

Selects phone number to be dialed. Works

with ORA

FEATURES

• Supports Standards CCITT V.22bis, V.22, Bell 212,

and Bell 103

• FCC Part 68 approved and DOC approvable

• Does not require a microprocessor to operate

• Pin activated hang-up

• Pin activated answer

• Manual originate and answer pins

• AT Command structure available

• UL1459 Recognized

• 1000 VAC isolation barrier, 1500V peak isolation

• Single 5 volt operation

• Low power sleep mode

• Automatic adaptive and fixed compromise

equalization

• Test modes and diagnostics

• Size: 2.0” X 1.25” X 0.53”

• NVRAM allows storage of custom configurations

and telephone numbers

• Commercial operating temperature: 0° to 70°C

• Extended temperature: –40° to 85°C (CH1787ET)

Figure 1. CH1787 Functional Block Diagram.

DAA. The CH1787 is designed to meet North

American telephone standards as set by FCC Part 68

and DOC. The telephone line interface meets UL1459

with 1000VAC and 1500 volt peak surge isolation. As

such, it complies with U.S., Canadian, and other

international requirements that specify that level of

isolation. The CH1787 is FCC Part 68 pre-approval. A

label is provided with the registration number and ringer

equivalent (REN). This label should be prominently

displayed on the host equipment. As with most

2002 Cermetek Microelectronics, Inc.

Page 1

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

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