National Instruments 3.22E+04 用户手册
Chapter 2
Installation and Verification
© National Instruments Corporation
2-15
Connecting Two-Wire Devices
The PCI-485 boards are designed to work with either two- or four-wire
devices. If you are using a two-wire device, refer to the device
documentation for specific wiring instructions.
devices. If you are using a two-wire device, refer to the device
documentation for specific wiring instructions.
In general, half-duplex networks use a single twisted pair of wires for
communication in both directions, so you must connect both the transmitter
and the receiver at each end of the same pair of wires. For example, to
connect an RS-485 data acquisition device to a port on your PCI-485 using
half-duplex communication, you need a single twisted pair of wires. At the
PCI-485, connect the TXD+ and RXD+ signals (pins 8 and 4 on a
DB-9 connector, pins 5 and 20 on a DB-25 connector) together and to one
wire. Connect the other end of this wire to both the TXD+ and RXD+
signals on the data acquisition device. Use the same method to connect the
TXD– and RXD– signals (pins 9 and 5 on a DB-9 connector, pins 22 and 7
on a DB-25 connector) to the second wire.
communication in both directions, so you must connect both the transmitter
and the receiver at each end of the same pair of wires. For example, to
connect an RS-485 data acquisition device to a port on your PCI-485 using
half-duplex communication, you need a single twisted pair of wires. At the
PCI-485, connect the TXD+ and RXD+ signals (pins 8 and 4 on a
DB-9 connector, pins 5 and 20 on a DB-25 connector) together and to one
wire. Connect the other end of this wire to both the TXD+ and RXD+
signals on the data acquisition device. Use the same method to connect the
TXD– and RXD– signals (pins 9 and 5 on a DB-9 connector, pins 22 and 7
on a DB-25 connector) to the second wire.
For information about setting the transceiver mode for two-wire
communication, refer to Chapter 4,
communication, refer to Chapter 4,
. For more
information about duplex architectures, refer to Appendix A,
Table 2-5. 100-Pin Connector Pin Descriptions
100-Pin Connector Port
232
Signal
232
D-Sub 9
Connector
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
2
46
6
42
10
38
14
34
—
—
—
—
—
—
—
—
DCD*
1
3
47
7
43
11
39
15
35
18
32
20
30
22
28
24
26
RXD
2
4
48
8
44
12
40
16
36
19
33
21
31
23
29
25
27
TXD
3
5
49
9
45
13
41
17
37
—
—
—
—
—
—
—
—
DTR*
4
1
1
1
1
50
50
50
50
51
51
51
51
100
100
100
100
GND
5
52
96
56
92
60
88
64
84
—
—
—
—
—
—
—
—
DSR*
6
53
97
57
93
61
89
65
85
68
82
70
80
72
78
74
76
RTS
7
54
98
58
94
62
90
66
86
69
83
71
81
73
79
75
77
CTS
8
55
99
59
95
63
91
67
87
—
—
—
—
—
—
—
—
RI*
9
* These signals are not supported on ports 9-16 of the 16-port PCI serial boards.