13: Modbus
Note: Modbus applies only to EDS4100, as this feature is not supported on EDS8/16/ 32PR and EDS8/16PS.
Modbus ASCII/RTU based serial slave devices can be connected via the ethernet through an existing Modbus TCP/IP network. Any device having access to a given Modbus implementation will be able to perform full range of operations that the implementation supports. Modbus/TCP use a reserved TCP port of 502 and include a single byte function code (1=255) preceded by a 6 byte header:
Table 13-1 6 Byte Header of Modbus Application Protocol
Transaction ID (2 bytes) | Identification of request/response transaction - copied by slave |
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Protocol ID (2 bytes) | 0 - Modbus protocol |
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Length (2 bytes) | Number of following bytes includes the unit identifier |
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Address (1 byte) | Identification of remove slave |
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Serial Transmission Mode
Evolution products can be set up to communicate on standard Modbus networks using either RTU or ASCII. Users select the desired mode and serial port communication parameters (baud rate, parity mode, etc) during the line configuration.
Table 13-2 Modbus Transmission Modes
RTU | ASCII |
Address: 8 bits (0 to 247 decimal, 0 is used | Address: 2 CHARS |
for broadcast) | Function: 2 CHARS |
Function: 8 bits (1 to 255, 0 is not valid) | Data: N CHARS (N=0 to 252 CHARS) |
Data: N X 8 bits (N=0 to 252 bytes) | LRC Check: 2 CHARS |
CRC Check: 16 bits |
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The Modbus web pages allow you to check Modbus status and make configuration changes. This chapter contains the following sections:
Modbus Statistics
Modbus Configuration
EDS User Guide | 109 |
