User's Guide

The Hardware View SB300 Series
Page 90 Proprietary and Confidential 2110059 Rev 1.1
Table 10-8: Serial Interface Electrical Characteristics
Characteristic Min.(V) Max.(V)
Input Low Voltage -0.3 0.8
Input High Voltage 2.5 5.0
Output High Voltage (Ioh=400 µA) 2.4 –
Output Low Voltage (Iol=3.2 mA) – 0.5
Serial Port Interface
The serial port pins comprise a standard set of serial data and handshaking lines. All signals are
negative assertion, HCMOS logic compatible. These signals must be terminated properly if they
are not used. Unused input signals must be pulled to the appropriate in-active state through a
resistor (10k). Unused output signals may be left unterminated. If a signal may have use as an
input or an output (I/O) then treat it as an input for termination purposes.
Hardware handshaking should be enabled using \CTS and \RTS as the primary flow control
signals. The remaining handshaking lines (\DCD, \DTR, \DSR, and \RI) are, strictly speaking, not
needed; however they are desirable for TCP/IP stack usage and are supported for any applications
that may require them.
Operation in each mode is as follows:
• \RTS, \CTS
Used as standard hardware flow control lines.
• \DTR
Indicates to the modem that the host device is active. This line may also be configured to
switch the modem from data to command state or reset the modem (AT&D), and to enable
host wake-up. See the RI description below.
• \DCD
Is asserted in CDPD mode while online with an active session. Behaviour options in CSC
and Wireline modes are set with the command AT&C.
• \DSR
Always active when the modem is on; it is tied to logic GND.
• \RI
In Wireline and CSC modes, this line toggles when there is an incoming call (the telephone is
ringing).
In CDPD mode, using UDP or TCP packet service, \RI toggles with a 1s on : 4s off duty cycle
when there is data for the host or a TCP connection request. If \DTR is inactive (high), the
\RI signal will go active through three cycles; otherwise it will go active once only. This is
repeated for each incoming packet or connection request until a session is opened. This signal
may be used to wake-up the host.
The serial port should be configured for 8-data bits, no parity bits, and 1-stop bit. Although the
current firmware release (R1.0.1) is fixed at 19200 bps, the eventual default DTE configuration
will auto-baud to the host serial baud rate (based on speed of the ‘A’ in an AT command). Host
data rates of up to 115,200 bps will be supported. AT commands may be used to fix the baud rate
from 110 bps to 115,200 bps.
In Circuit-Switched mode data state and any mode’s command state, a terminal emulation
program may be used to communicate with the modem and change the configuration.