Chapter 2 Hardware Installation and Configuration©National Instruments Corporation2-9FieldPoint FP-1000/1001 User ManualAn alternative method is to connect the FP-1001 directly to your hostcomputer, if your host computer provides an RS-485 interface. ContactNational Instruments for information about available RS-485 hardware.You can connect up to 25 FP-1001 network modules to each RS-485port on the host computer. This network configuration method is shownin Figure 2-10.Figure 2-10. Host Computer Connected to Three FP-1001 Network ModulesWhen the FP-1001 is cabled directly to an RS-485 port on a hostcomputer, as shown in Figure 2-10, you can wire it in either 4-wire fullduplex mode or 2-wire half duplex mode.The multidrop topology used by the RS-485 network in these twonetworking configurations protects against power failures at individualFieldPoint banks. It eliminates the possibility that a power failure at oneFP-1001 bank might affect the communication between other banks inyour network. Because the FP-1000 provides an RS-485 repeater, apower failure at that bank affects communications.Caution: Do not use the isolation barrier of the RS-485 interface as a way to protecthuman contact from common-mode voltages of more than 250 Vrms. TheRS-485 interface on both the FP-1000 and the FP-1001 modules is isolatedfrom the rest of the FieldPoint system, including the power supply,backplane, and the RS-232 interface on the FP-1000. It is isolated with agalvanic and optical isolation barrier, which has been designed and testedto withstand fault voltages of up to 2500 Vrms. However, the safety ratingof this barrier is only for working voltages of up to 250 Vrms. Also note thatwhile the RS-232 interface on the FP-1000 is isolated from the RS-485Host Computer withRS-485 Board InstalledFP-1001FP-1001FP-1001RS-485!
