© 2000 Cermetek Microelectronics, Inc.
Page 3 Document No. 607-0017 Rev. B (06/00)
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.
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 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.
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.
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.
Increasing numbers correspond to higher volume. Figure 3 indi-
cates one method of driving an external 8 ohm speaker.
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
Bell 103
CCITT V.22
Bell 212A
CCITT V.22bis
CCITT V.32
CCITT V.32bis
CCITT V.34
CCITT V.34bis
CCITT V.90
The Modulation/Demodulation scheme supports the industry
modem standards listed below.
