Chapter 2
Hardware Installation and Configuration
©
National Instruments Corporation
2-9
FieldPoint FP-1000/1001 User Manual
An alternative method is to connect the FP-1001 directly to your host
computer, if your host computer provides an RS-485 interface. Contact
National Instruments for information about available RS-485 hardware.
You can connect up to 25 FP-1001 network modules to each RS-485
port on the host computer. This network configuration method is shown
in Figure 2-10.
Figure 2-10. Host Computer Connected to Three FP-1001 Network Modules
When the FP-1001 is cabled directly to an RS-485 port on a host
computer, as shown in Figure 2-10, you can wire it in either 4-wire full
duplex mode or 2-wire half duplex mode.
The multidrop topology used by the RS-485 network in these two
networking configurations protects against power failures at individual
FieldPoint banks. It eliminates the possibility that a power failure at one
FP-1001 bank might affect the communication between other banks in
your network. Because the FP-1000 provides an RS-485 repeater, a
power failure at that bank affects communications.
Caution:
Do not use the isolation barrier of the RS-485 interface as a way to protect
human contact from common-mode voltages of more than 250 Vrms. The
RS-485 interface on both the FP-1000 and the FP-1001 modules is isolated
from the rest of the FieldPoint system, including the power supply,
backplane, and the RS-232 interface on the FP-1000. It is isolated with a
galvanic and optical isolation barrier, which has been designed and tested
to withstand fault voltages of up to 2500 Vrms. However, the safety rating
of this barrier is only for working voltages of up to 250 Vrms. Also note that
while the RS-232 interface on the FP-1000 is isolated from the RS-485
Host Computer with
RS-485 Board Installed
FP-1001
FP-1001
FP-1001
RS-485
!
