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CH2156

HIGH SPEED INTERNET MODEM FAMILY

Cermetek Microelectronics 

The modem communicates over the serial interface with the host

processor (referred to as a DTE or Data Terminal Equipment) at a

fixed speed regardless of the carrier line modulation speed (DCE)

of the PSTN modem connection. This eliminates the need to

have the DTE step up or step down in speed based on the

incoming or outgoing PSTN communication data rate.

Non-Volatile RAM (NVRAM).

NVRAM can store two user-customized configurations. The

AT&Wn command will store the active modem 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 modem configu-

rations to be automatically recalled and made active upon reset

or power up. The ATZn command immediately recalls and

activates a stored configuration. See Tables 7A and 7B for

storable S-Registers and Commands. The NVRAM can save up

to four telephone numbers, with up to 36 digits or modifiers in

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

telephone number dial string. The ATDS=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

Telephone Line Interface or DAA.

High performance modems are extremely sensitive to DAA (Data

Access Arrangement) performance. The difference between a

good modem and a fair one is in the DAA performance. The

iModem® family includes a unique low distortion DAA designed

for optimal performance over all PSTN line conditions thereby

achieving the most reliable and best performance PSTN connec-

tions.

The iModem® family is designed to meet North American

telephone standards as set by FCC Part 68 (USA) and CSA CS-

03 Part I (Canada). The PSTN line interface is UL1950 and CSA

C22-2 950 Listed (Third Edition) and is designed to meet 1500

VAC RMS isolation and provide 2122V peak surge protection.

Consequently, the iModem® family of products satisfies U.S. and

Canadian requirements, and will meet other international ap-

proval agency requirements that specify these levels of isolation.

Pins 1 and 2 function as both input and output connections to the

PSTN. To maximize field reliability in hostile environments, for

Canadian approval, for UL compliance, and also optionally for

FCC Part 15 compliance, these two pins must be routed through

an external network such as that described in Figure 6A and in

Cermetek Application Note #126.

Each iModem® product comes with FCC Part 68 approval and is

shipped from the factory with an FCC label indicating registration

number and ringer equivalent. This label should be prominently

displayed on the end product. With the exception of the U.S.,

most countries (including Canada) require submission of the final

product or system containing the iModem® to the appropriate

governing regulatory agency for approval.

Typically this is accomplished by submitting the final end product

to an independent test house or consultant for evaluation. The

test/consultant then forwards the test results and applicable

documents to the regulatory agency. Contact Cermetek for a list

of suggested consultants.

Modulation/Demodulation/Error Correcting and Data

Compression

These functions are provided by an industry standard modem

ship set which has been adapted for use with the iModem®

Family.

Bell 103

Bell 212A

CCITT V.22

CCITT V.22bis

CCITT V.32

CCITT V.32bis

CCITT V.34

CCITT V.34bis

CCITT V.90

The iModem® supports V.42 LAMP, MNP 2-4, MNP 10 error

correcting protocols and uses V.42bis data compression, allowing

data transmission rates of up to a maximum of 230.4kbps. These

high DTE data rates are supported by the iModem® serial inter-

face via its auto baud capability. Note that the maximum speed

attained is limited by the maximum speed available from the DTE

and not by the iModem®.

When the iModem® is operating in the internet state, all iNet AT®

Command communication between the iModem® and the host

processor (DTE) is conducted over the RS232 serial interface at

57.6kbps. When the iModem® is operating in the modem state,

communication with the DTE can be at any speed up to, and

including, 230.4kbps.

The resident Modulator/Demodulator supports line equalization and

forward error correction.

CONNECTING TO THE HOST UART

Since a modem communicates data serially and most host products

handle data in a parallel format, a UART is needed to make parallel-

to-serial and serial-to-parallel translations.

SUPPORTED FEATURES

Standard AT Command Set.

The iModem® supports the standard Hayes AT Command set with

extensions and can operate with industry standard communication

software. The AT commands are compatible with TR302.2/88-

08006. Refer to Table 6A & 6B for the command set description.

iNet AT® Command Set.

Cermetek has created a set of iNet AT® command extensions for

control of the internet communication function. These commands

operate in the same fashion as the standard AT commands. Refer

to Table 6C for the iNet AT® command extension set.

Serial Host Interface.

The iModem® operates in asynchronous mode and supports both

the full RS-232C/V.24 serial interface and a 5V, RS232-like interface

called V.24 (EIA-232-E). Signal levels are TTL rather than RS-232V

level compatible, which allows direct connection of the iModem® to

the host’s UART without level translating circuitry. See Table 3 for a

complete set of pin descriptions.

The iModem® is controlled by sending serial commands over TXD

and by monitoring serial status messages returned on RXD. All

other serial interface lines may be utilized for the convenience of a

particular application but are not required by the iModem®. Unused

outputs from the iModem® should be left unconnected. Unused

inputs should be tied to the proper logic level. See Table 3.

When using the iModem® exclusively in an event driven application,

the serial interface is not required.

Speaker Interface.

The SPK output reflects the receiver analog input and provides a

signal test that can be used to monitor call progress. The SPK

signal can drive a 300 ohm 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 ATLn command,

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

The Modulation/Demodulation scheme supports the industry

modem standards listed below.

© 2000 Cermetek Microelectronics, Inc.

Increasing numbers correspond to higher volume. Figure 3 indi-

cates one method of driving an external 8 ohm speaker.

Page 3

Document No. 607-0017 Rev. B (06/00)

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