Lantronix EDS8PS EDS - User Guide - Page 109
: Modbus, Serial Transmission Mode
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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) Protocol ID (2 bytes) Length (2 bytes) Address (1 byte) Identification of request/response transaction - copied by slave 0 - Modbus protocol Number of following bytes includes the unit identifier Identification of remove slave 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 Address: 8 bits (0 to 247 decimal, 0 is used for broadcast) Function: 8 bits (1 to 255, 0 is not valid) Data: N X 8 bits (N=0 to 252 bytes) CRC Check: 16 bits ASCII Address: 2 CHARS Function: 2 CHARS Data: N CHARS (N=0 to 252 CHARS) LRC Check: 2 CHARS 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