Cermetek
microelectronics
CH1787 Small Functional Modem
INTRODUCTION
The CH1787 is a small full function modem that is FCC Part
68 approved. It has been designed to be used in
applications where there is little or no controller intelligence
to command the modem. This allows the user to operate
the modem via hardware resources only, not requiring AT
Command execution for basic operation. For those
applications where there is controller intelligence, the
CH1787 operates like a standard AT Command driver
2400bps, V.22bis asychronous modem.
The CH1787 is ideal as a remote modem such as found in
alarm products and in industrial controllers. Upon some
operational event, the modem will dial a prestored telephone
number under pin activation to make a modem connection
with a host or another site. The modem can also be set to
automatically answer incoming calls or manually answer a
call, using an answering pin. A call can be ended via a
hang-up pin.
GENERAL DESCRIPTION OF FUNCTIONAL
BLOCKS
Figure 1 is a functional block diagram of the CH1787. Each
block will be described. The CH1787 is a highly integrated,
full function modem, comprised of a modulator/demodula-
tor, controller, and an FCC Part 68 approved telephone in-
terface, also called a 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 in-
tegrated AT command control and resident interfaces for
general communication and routing to the DAA.
Controller
The controller is a programed microprocessor that provides
commands to the modem in response to external pin acti-
vation. The following pins are controlled by the micropro-
cessor and are described in detail in Table 1. These pins
are operational when the modem is in use at 2400bps only.
ANS - Manual Answer Pin Input - Answer mode-
Places modem in answer mode
ORG - Manual Originate Pin Input - Originate mode -
places modem in originate mode
ORA- Automatic Dial Pin Input - Dials one of two
prestored numbers based on TST
TST - Steering Pin Input used with ORA to select the user
stored number or Cermetek test number
HNG- Hang-up Pin Input used to terminate an active
modem connected
AAR- Automatic Answer Pin - used to place the modem
in Auto Answer Mode
See pin description Table 1 for more details.
Cermetek Microelectronics, Inc.
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
1000 VAC isolation barrier
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
Operating temperature 0o-70oC
Extended temperature -40oC to 85oC order
CH1787ET
Figure 1. CH1787 Functional Block Diagram
Document No. 603-0182 Rev. D (11/98) 1