RADIUS
Product
Description
PDR221
iom_pdr221_04_r02.doc
Rev 02
Page 30 (60)
9.4 Serial Interface
The PDR221 is connected to the control system / RTU via the RS-232 interface.
The serial data transmission is full duplex with selectable data speeds between 600 and 19200
bps, with or without parity. See chapter 12.7 for configuration.
9.4.1 PDR221 Serial Interface Characteristics
Pin
Number
Input /
Output
Description
1
Out
DCD – Data Carrier Detect
The DCD signal is always high/active during transmission of serial data to
connected device. The PDR221 can be configured to activate the DCD before
and after transmission of the serial data. Pre- and Post DCD. See also
configuration chapter 12.7.
2
Out
RxD – Received Data
Transmits received data to the connected device.
3
In
TxD – Transmitted Data
Receives transmitted data from the connected device.
4
In
DTR – Data Terminal Ready
Not used by the PDR221.
5
-
GND – Signal Ground
6
Out
DSR – Data Set Ready
Always active/high when in normal operation mode. DSR is deactivated/low
when PDR221 is in configuration mode. I.e. not ready to receive data on the
serial port.
7
In
RTS – Request To Send
Used for EOM, End Of Message, detection if selected in configuration.
The connected device sets RTS high when a message is to be transmitted.
When the last byte is transmitted, the RTS is set low. This negative flank is
used by the PDR221 to detect EOM. See 9.4.3.
8
Out
CTS – Clear To Send
The CTS signal is active/high when the PDR is ready to receive data.
It is deactivated/low from when a message is completely received on the serial
port until the message is completely transmitted on the radio. It is also
deactivated/low from when a message is detected on the radio until it is
completely transmitted on the serial interface..
Note!
It is not necessary to use the CTS signal. Though, it can be used to
avoid data transfer collisions in some systems.
9
Out
RI – Ring Indicator. Not used by the PDR221. (Used by DCE telephone
modem equipment. Indicates ring signal on a telephone line).
Table 1. Serial data interface connector pinout
It is not necessary to wire any handshaking signals to receive data telegrams from connected
equipment. Only the TxD, RxD and GND signals need to be connected. Though, the unit offers
status and handshaking signals that can be used by the control system if necessary. The RTS
signal shall be wired if it shall be use for EOM (End Of Message) detection, see chapter 9.4.3.
Note!
The PDR221 radio operates as a DCE, (Data Communication Equipment). Check how the
connected device and/or control system operates, DCE or DTE (Data Terminal Equipment), to
select the correct serial cable configuration.
Note!
Depending on the functionality of the connected device, it is sometimes required to jump-
wire the handshaking signals, DTR/DSR, RTS/CTS, as cable types 3 and 6 below. However, it is
most often possible to use a “three wire connection” like cable type 2 below.
Standard 9 wire pin-to pin serial cables are configured as cable type 1 below.