Campbell CDM-A100 Series, Instruction Manual

Page: 32 / 61

CDM-A100 Series
21
The CPI port on CDM-A100 connects directly to the CPI port on the CR6. An
SC-CPI
(p. 33)
device is required to connect to CR800-series, CR1000, and
CR3000 dataloggers. Connect the SC-CPI module to these dataloggers by
wiring its 12V, G, C1, C2, and C3 terminals to the corresponding 12V, G, C1,
C2, and C3 terminals of the datalogger. Connect a CPI port on the CDM-A100
to the CPI port on the SC-CPI.
7.6 Connecting Multiple CDMs
The CPI
(p. 32)
bus, which handles the communication between the datalogger
and CDMs, can accept addresses 1 – 120. Multiple CDMs may be connected to
a single datalogger using a daisy-chain or star topology. In both network
configurations, as total cable length increases, the maximum possible bit rate
decreases. Therefore, in networks with long cable lengths, it may be necessary
to use the CPISpeed() instruction to decrease the CPI network bit rate from its
default 250 kbps. Limitations on cable length and bit rate are discussed further
in Section
8.2.2 , CPI Network Bit Rate
(p. 28)
and listed in TABLE 8-2 , Network
Topology, Bit Rate, and Cable Length
(p. 28)
.
7.6.1 Daisy-Chain Topology
In a daisy-chain topology, CDM-A100s are connected one after another. An
illustration of this is shown in FIGURE
7-1 .
FIGURE 7-1. Multiple CDM-A108s connected in a daisy-chain topology
For maximum system performance, insert a termination resistor plug (pn
28558) in the last open CPI port of the CPI bus.
7.6.2 Star Topology
A star topology uses a passive RJ45 hub, such as the HUB-CPI 8-Channel
RJ45 Hub for CPI Peripherals (pn 30692), to connect multiple CDM-A100s.
An illustration of this is shown in FIGURE
7-2 . This configuration does not
allow termination resistor plugs.
FIGURE 7-2. Multiple CDM-A108s connected in a star topology
Datalogger/SC-CPI CDM-A108 CDM-A108 CDM-A108 CDM-A108