User manual

13
Signal
Direction
Limits
Description
7
RTS
Input
> + 2,4V
< 0.8 V
Request to send
8
CTS
Output
> + 4V
< - 4 V
Clear to send
9
RI
Output
> + 4V
< - 4 V
Ring indicator
Table 5: Electrical characteristics of the serial port signals
2.5.1 Serial Data
The modem supports the standard data character format of
 Programmable baud rate
 Auto-configuration mode with auto-baud.
2.5.2 Serial Data Signals
Serial Data From Modem (RD)
RD is an output signal that the modem uses to send data to the application.
Serial Data To Modem (TD)
TD is an input signal, used by the application to send data to the modem.
2.5.3 Control Signals - RTS, CTS, DTR, DSR, DCD, RI
Request to Send (RTS)
RTS is used to condition the DCE for data transmission. The default level is high by internal pull
up. The exact behaviour of RTS is defined by an AT command. Software or Hardware control
can be selected. Hardware flow is the default control. The application must pull RTS low to
communicate with the modem. The modem will respond by asserting CTS low, indicating it is
ready for communication.
Clear To Send (CTS)
CTS indicate that the DCE is ready to transmit data. The default level is high. You can define
the exact behaviour of CTS through an AT command, and can select software or hardware flow
control.
Data Terminal Ready (DTR)
DTR indicates that the DTE is ready to transmit and receive data. It also acts as hardware
‘hang-up’, terminating calls when switched high. The signal is active low. You can define the
exact behaviour of DTR with an AT command. The DTR line can also be used to switch on the
modem when activated for 0.2 seconds. The DTR line must be deactivated prior to switching
off the modem to ensure it switches off (powers down) correctly.
Data Set Ready (DSR)
An active DSR signal is sent from the modem to the application (DTE) to confirm that a
communications path has been established. DSR has two modes of operation, settable using
the AT command AT&S.