B&B Electronics MAP450D - Manual (Page 10)

2.3. RS-422/485 (Network mode)
Network mode supports the 3-wire and 5-wire RS-422/485 configurations. The
3-wire configuration has both transmit and receive on the same pair of wires plus a
signal common. The 5-wire configuration has differential signal pairs for transmit
and receive plus a signal common. In both configurations the signal pairs must be
twisted and surrounded by an overall shield.
NOTE: When using 3-wire RS-422/485, Jumper JP4 must be in position “B”.
Refer to section 2.4 for instructions.
5-wire RS-422/485 supports full-duplex communications; which means that the
host controller can trasmit data to the OITs and receive data from the OITs at the
same time. 3-wire RS-422/485 only supports half-duplex communications; which
means that the host controller cannot transmit and receive data at the same time.
Although 3-wire RS-422/485 installations may be less costly than 5-wire
installations, the increased complexity in programming the host controller for
3-wire RS-422/485 may increase development time.
10 MAP450D
1010-0046A, REV 00
5
COM
RXD+
RXD-
+24V
3
4
2
1
TB1
Shield
OIT
From or To
Host or OIT
+24V
GND
Power Supply
RTN 8
*
*
RTN and COM are internally connected in OIT. *
7
TXD+
TXD- 6
CHASSIS GND
RXD+/TXD+
RXD-/TXD-
SIG GND
SIG GND
Figure 5 3-Wire RS-422/485 (Network mode)
5
COM
RXD+
RXD-
+24V
3
4
2
1
TB1
Shield
OIT
From or To
Host or OIT
+24V
GND
Power Supply
RTN 8
*
*
RTN and COM are internally connected in OIT. *
7
TXD+
TXD- 6
CHASSIS GND
TXD+
TXD-
RXD-
SIG GND
RXD+
SIG GND
Figure 6 5-Wire RS-422/485 (Network mode)