Campbell Scientific MD485 RS-485 Multidrop Interface User Manual
Page 16
MD485 RS-485 Multidrop Interface
active ports, while the remote MD485 has the active ports set to RS-485 and
CS I/O. With the MD485s configured as transparent devices, the only protocol
limitation is the fact that RS-485 is a half-duplex interface. If used with
traditional datalogger communication, PC software must take the half-duplex
nature of the link into account. For array-based dataloggers, this is
accomplished by PC400, LoggerNet, or PC208W.
RS-232
RS-485
CS I/O
To Wall Transformer
FIGURE 8. Long Distance RS-232 to CS I/O Conversion
Figure 9 shows how an MD485 could be used to send one-way data to a serial
printer via a P96 instruction. A null modem may be required in the RS-232
line for the printer. A transformer would be needed to power the MD485
nearest the printer, because the MD485 is not port-powered from the RS-232 or
RS-485 ports. In this configuration, the MD485 near the datalogger has CS I/O
and RS-485 as active ports. The CS I/O port should be configured to
Addressed Print Device which emulates a CSI SC99. RS-485 and RS-232 are
the active ports for the MD485 near the printer. Since printer data is one-way
only, the fact that the RS-485 interface is half-duplex is not an issue.
SE
DIFF
G
G
H
L
1
2
1
AG H
L AG H
L AG E1
AG E2 G
3
4
2
5
6
3
SE
DIFF
G
G
H
L
7
8
4
AG H
L AG H
L AG E3
AG G
G
9
10
5
11
12
6
P1 G P2
G C8 C7 C6 C5 C4 C3 C2 C1
G 12V 12V
SDM
5V 5V G
G
SW 12V
SW 12V CTRL
Logan, Utah
G 12V
G 12V
POWER
IN
CR10X WIRING PANEL
MADE IN USA
WIRING
PANEL NO.
EARTH
GROUND
CS I/O
CS I/O
RS-485
Null Modem Cable
To Wall Transformer
FIGURE 9. MD485 to Serial Printer
Figure 10 shows the MD485 used in a point-to-multipoint configuration. With
the MD485s in transparent mode, only a master-slave protocol is supported.
MODBUS is the only such protocol supported by CSI dataloggers and
commonly used in the SCADA industry.
10