Cermetek Microelectronics, Inc.
High Speed Modem and FAX Family
2003 Cermetek Microelectronics, Inc.
Page 2
Document No. 607-0003 Revision K3 (09/03)
Equipment (DTE) 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
in-coming or out-going PSTN communication data
rate. Hence, the DTE can train the CH2056, to say
56kbps, and talk to a slower in-coming data
connection at say, 2400bps without changing host
speed. Conversely, the host DTE trained at 14.4kbps
can also communicate with the modems at higher
speeds, say 28.8kbps. This is accomplished by
invoking internal automatic data flow control. The HS
Modem family has a resident buffer to allow for this
auto baud operation.
Non-Volatile RAM (NVRAM).
NVRAM can store
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 configurations 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 31 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 HS Modem 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 connections.
The HS Modem family is designed to meet North
American telephone standards as set by the FCC Part
68 (USA) and CSA CS-03 Part I (Canada). Among the
more critical parameters, the PSTN line interface is
designed to meet 1500 VAC RMS isolation and
provide 2122V peak surge protection. Consequently,
the HS Modem family of products satisfies U.S. and
Canadian requirements, and will meet other
international approval agency requirements that
specify these levels of isolation. The TBR/ETBR
variants also meet the European TBR21 requirements.
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 briefly described in
Figure 6A and described in more detail in Cermetek
Application Note # 126.
Each HS Modem 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 HS
Modem 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
house/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 chip set which has been
adapted for use with the HS Modem family. The
Modulation/Demodulation scheme supports the
industry modem standards listed below.
SUPPORTED MODULATION STANDARDS
Bell 103
CCITT V.22
Bell212A
CCITT
V.22bis
CCITT
V.32
CCITT
V.32bis
CCITT
V.34
CCITT
V.34bis
CCITT
V.90
The HS Modem supports V.42 LAMP, MNP 2-4, MNP
10 error correcting protocols. The CH1794 uses
MNP5 data compression techniques and the
CH1799/CH2056 uses V.42bis data compression,
allowing data transmission rates of up to a maximum
of 57.6kbps/115.2kbps/230.4kbps, respectively.
These high DTE data rates are supported by the HS
Modem serial interface via its auto baud capability.
Note that the maximum speed attained is limited by
the maximum speed available from the DTE.
The resident Modulator/Demodulator supports line
equalization and forward error correction.
IMPORTANT NOTE
The V.90 standard prescribes 56kbps
downlink and 33.6kbps uplink. Consequently,
two V.90 modems connected back-to-back will
send at 33.6kbps.
