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1、 1 2011 American Power Conversion All rights reserved No part of this publication may be used reproduced photocopied transmitted or stored in any retrieval system of any nature without the written permission of the copyright owner Rev 2011 0 Abstract This application note explains how to install the
2、 Modbus wiring for an AP9635 Network Management Card gives an overview of the Modbus protocol describes the Modbus packet structure and explains how to identify and resolve common problems Introduction The Modbus standard defines both hardware and protocol The hardware media is based on RS 485 with
3、certain additional constraints RS 485 communications can be half duplex over a 2 wire bus or full duplex over a 4 wire bus RS 485 is differential signaling multi drop typically up to 32 devices on a bus however repeaters are available to extend this and designed for long distances up to 4000 ft 1220
4、 meters It must be a linear bus not a star When interconnecting in environments where ground potential differences may exist such as power devices or over significant distances devices with isolated communications ports should be used 4 wire Connection Diagram By Gary Ware APC APPLICATION NOTE xx AP
5、C Modbus Installation and Troubleshooting for AP9635 Network Management Card 2 2011 American Power Conversion All rights reserved No part of this publication may be used reproduced photocopied transmitted or stored in any retrieval system of any nature without the written permission of the copyright
6、 owner Rev 2011 0 APC APPLICATION NOTE 2 wire Connection Diagram Wiring Guidelines Good quality shielded twisted pair cable should be used Shielded cable is worth the small added cost Wiring should be done in accordance with local wiring codes Do not put communications cables and power cables in the
7、 same raceways or conduits Route communications cables to avoid potential noise sources such as high power equipment or motors In addition to the 2 or 4 signal lines the common terminal should be connected at each device and the shield should be connected to chassis at each device Common should not
8、be connected to chassis The common connection requires an extra twisted pair in the cable a total of 2 twisted pairs for a 2 wire bus and 3 twisted pairs for a 4 wire bus The shield should be connected to each device not just at one end It should be earth grounded at one point in the system The AP96
9、35 represents 0 5 standard Modbus loads The AP9635 Modbus port is optically isolated The Modbus port s ground is not connected to any other ground AP9635 requires two 3 contact connectors provided APC Part 730 0532 Phoenix Contact part number 1952270 FMC 1 5 3 ST 3 5 The Modbus standard specifies 15
10、0 ohm termination resistors at each end of a bus Unless the bus is very long and operating at high data rates these resistors are not needed and in fact they reduce the signal swing and therefore reduce noise immunity Busses under 2000 feet operating at 9600 baud or under 1000 feet operating at 19 2
11、00 baud should not require termination 3 2011 American Power Conversion All rights reserved No part of this publication may be used reproduced photocopied transmitted or stored in any retrieval system of any nature without the written permission of the copyright owner Rev 2011 0 APC APPLICATION NOTE
12、 The standard also specifies bias resistors of 400 650 ohms which are normally placed at the system controller or supplied inside the controller one from D0 to ground and one from D1 to 5VDC Setup and Configuration Modbus requires that every setting be correct for communications to take place This i
13、ncludes Baud rate typically either 9 600 or 19 200 Number of data bits must be 8 Parity typically either none or even Number of stop bits typically 1 for even parity or 2 for none Device address in the range of 1 to 247 every device must be different Every device on the bus must have exactly the sam
14、e settings except the device address which must be unique for every device No two devices on the bus can have the same address Serial settings are often abbreviated For example 9600 8 N 1 means 9600 bits sec 8 data bits no parity 1 stop bit For the AP9635 card the Modbus configuration can be found b
15、y accessing the web page The IP address of the card is used for access to the web page so the card must be connected to a network via the Ethernet port and must get an IP address either by static configuration or dynamically via DHCP One way to view and set this information is via the console port o
16、n the card This configuration option uses a special cable APC 940 0299A supplied with the card Connect the cable to the DB9 serial port on a laptop and plug the mini plug into the Console port on the card Use a dumb terminal program e g HyperTerminal or PuTTy set to 9600 N 8 1 Press Enter 2 or 3 times or until you see the prompt Username Enter your username the default is apc and for the prompt Password enter your password the default is apc At the APC prompt type tcpip If the IPv4 Address is no
