CH1794A Cermetek Microelectronics, CH1794A Datasheet - Page 3

• Manufacturer Part Number: CH1794A
• Manufacturer: Cermetek Microelectronics

Specifications of CH1794A

• Lead Free Status / RoHS Status: Not Compliant

Cermetek Microelectronics, Inc.
Error Correction. Error correction is enabled via the
\Nn command.
&Qn and sets S36 and S48 values.
Cermetek, “AT Commands and S-Registers”, for a
more detailed discussion.
The HS Modem supports V.42 LAPM, MNP 2-4, MNP
10 error correcting protocols.
MNP5
CH1799A/CH2056A uses V.42bis and V.44 data
compression, allowing data transmission rates of up to
a
respectively.
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.
Ring Indicator (RI). The RI pin follows the frequency
of the ring signal and toggles low when the modem
detects an incoming call. The ring signal is typically 20
to 30 Hz and is on for 2 seconds and off for 4 seconds.
Although not TTL compliant, the RI pin can,
nonetheless, be utilized to activate external circuitry
including the external RST pin.
Off-Hook Indicator (OHI). The “H” version of the HS
Modem provides an active high signal on the OHI pin
(Pin # 18) indicating when the HS Modem goes off-
hook. The circuit in Figure 2 can be used to drive an
external LED.
high) is 2.75-3.25 volts.
+MS Command.
automatic data rate function of the HS modems. This
is accomplished by executing the +MS command.
This command allows the user to specify the desired
data modulation protocol. Further, the +MS command
may be used to force a desired data rate and/or
restrict the allowed data rate.
modulation schemes are listed above.
The
modulation scheme:
Enter:
Result:
This is identical to the following explicit +MS
command:
Enter:
Result:
2007 Cermetek Microelectronics, Inc.
The V.92 standard prescribes 56kbps downlink and
48.8kbps uplink. Consequently, two V.92 modems
connected back-to-back will transmit at 48.8kbps
(maximum).
maximum
following
data
AT+MS=V22B
OK
AT+MS=V22B,0,300,1200,300,1200
OK
compression
These high DTE data rates are
Note that the OHI output active (or
IMPORTANT NOTE
of
examples
Enabling error correction overrides
The user may override the
57.6kbps/115.2kbps/230.4kbps,
establish
techniques
The CH1794A uses
The supported
the
and
Refer to
V.22bis
the
Page 3
Figure 2. Example of Off Hook Indication using
“H” version HS Modem and external LED and
resistor.
Refer to, “AT Commands and S-Registers”, for a more
detailed discussion of the +MS command.
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
AT Command Set. The HS Modem supports the AT
Command set with extensions and can operate with
industry standard communication software. The AT
Commands are compatible with TR302.2/88-08006.
Serial Host Interface.
operates in asynchronous mode and supports a 5V,
RS232- like interface called V.24 (EIA-232-E). Signal
levels are TTL rather than RS-232C level compatible,
which allows direct connection of the HS Modem to the
host’s UART without level translating circuitry. See
Table 3 for a complete set of pin descriptions.
The modem 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 modem.
Unused outputs from the HS Modem should be left
unconnected.
proper logic level. See Table 3.
The minimum transmission rate is not stored and will
default to 300bps upon execution of reset or upon
power up.
CH179XA/2056A High Speed Family of Ultra Small Modems
Unused inputs should be tied to the
Document No. 607-0020 Revision B (01/07)
NOTE
The HS Modem family