User manual

CEP AG Revision 1.3
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Page 12 of 28
The electrical characteristics of the serial port signals are shown below:
PIN Signal Direction Voltage levels Description
1 DCD Output
> + 4V
<- 4 V
Data carrier detect
2 RD Output
> + 4V
<- 4 V
Received data
3 TD Input
> + 2,4V
< 0.8 V
Transmitted data
4 DTR Input
> + 4V
< 0.8 V
Data terminal ready
5 GND - 0 V Ground connection
6 DSR Output
> + 4V
< - 4 V
Data set ready
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
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.