UM-0085-B09
DT80 Range User Manual
Page 197
RG
Connecting to the Serial Sensor Port
The DT80 serial sensor port terminals have different functions depending upon the configured serial standard (RS232,
RS422 or RS485).
Terminal
RS232
RS422
RS485
Wake
Tx Z
Transmit Data
Transmit Data– (A)
Data– (A)
Rx A
Receive Data
Receive Data+ (B)
RTS Y
Handshake output
Transmit Data+ (B)
Data+ (B)
CTS B
Handshake input
Receive Data– (A)
D GND
Signal Ground
Ground
Ground
Figure 77: The DT80’s Serial Channel terminals (DTE)
Note that:
•
The
RTS
and
CTS
handshake/control signals are available for RS232 only
•
The
DGND
terminal is the signal return (common) for RS232. RS422/ 485 use differential signalling – the
ground is not used as a reference, but it should still be connected to avoid excessive common mode voltages.
•
Activity on either of the indicated terminals (i.e.
Rx/ A
and
CTS/ B
) will wake the logger from sleep mode,
although the data in the particular message that woke the logger will be lost. Note also that if the Wake feature
is required and RS485 is being used then it will be necessary to link the Data terminals (
Tx/ Z
and
RTS/ Y
) to
the wake-enabled terminals (
Rx/ A
and
CTS /B
).
RS232 Connection
The serial sensor port is wired as a DTE device so the data lines must be "crossed over" when connecting to another
DTE device. That is, the DT80's
TxD
output connects to the sensor's
RxD
input, and vice versa.
The handshaking signals, if used, must also be crossed over, i.e.
RTS
connects to
CTS
and vice versa.
Figure 78: Serial sensor port RS232 connection. RTS/CTS connections are optional
A cable suitable for connecting the DT80 serial sensor port to a PC serial port may be ordered (dataTaker part number
CAB-015). See also
Serial Sensor Port null modem cable (P393)
.
RS422 Connection
RS422 allows for multi-drop connection, where one or more sensors are connected in parallel. The DT80 is typically the
"master" device in the network and is therefore wired so that its transmissions will be received by all slave devices. The
slaves' transmit lines are all tied together, which means that only one slave is permitted to transmit at any one time. It is
up to the communications protocol to ensure that this is the case – typically each slave will be assigned a unique address
and will only respond if it receives a request from the master that is addressed to it.
RS422 uses
full duplex
differential signalling: two wires for transmit (
Y
and
Z
) and two wires for receive (
A
and
B
). Be
sure to observe the correct signal polarity, as shown in the diagram. Some devices label their terminals as
A
or
B
, some
as + or –.
Figure 79: sensor port RS422 connection, assuming that the DT80 is the designated master device
