User manual

2004 Stevens Water Monitoring Systems Inc. All Rights Reserved.
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TxD—2
RxD—3
DSR—4
GND—5
DTR—6
CTS—7
RTS—8
RS232 Equipment—DCE
TxD—2
RxD—3
DSR—4
GND—5
DTR—6
CTS—7
RTS—8
RS232 Equipment—DCE
Null Modem Connection
Between DCE Equipment
Figure 15: Null Modem Connection: DCE
4.4 Connecting to RS485 Equipment
4.4.1 2-Wire vs. 4-Wire RS485
The Shark is capable of RS485 communication. The Shark operates with a 4-wire
RS485 system. A 4-wire RS485 system is called “Full-Duplex”, while a 2-wire RS485
system is called “Half-Duplex”
4.4.2 Full-Duplex vs. Half-Duplex
With a 4-wire RS485 system, the transmit lines are separated from the receive lines and
operated independently (2-wires for transmit and 2-wires for receive). Therefore,
transmit and receive signals can occur at the same time. This is called Full-Duplex.
With a 2-wire RS485 system, the transmit and receive lines time-share the same 2-wires.
During a receive block of data, the transmit driver is disabled. This is called Half-Duplex.