Getting Started with SMD & Modbus RTU Communications.pub
Contents
1. 2 Set BIT 8 of the Control Word to select Serial Speed Reference Modbus Master frame transmission 3 Set BIT 3 of the Control Word to enable the drive the drive display will change Modbus Master frame transmission ao o Code 4 Seta value of 250 to the serial speed reference register 40 The drive display will change to display the output frequency which will be 25 0Hz Modbus Master frame transmission i Function Code 0 06 5 Set BIT 2 of the Control Word to disable the drive the drive display will change to Inh for inhibit Modbus Master frame transmission U 4 _ O E L D j Lenze Lenze DS041 AC Tech2. Function Code Size 1 byte The function code indicates what kind of action to perform The function code depending upon the function is normally followed by a data field that contains request and response parameters e The SMD supports function codes 3 Read Holding Registers 4 Read Input Registers 6 Preset Single Register 16 Preset Multiple Registers Note In general the SMD is limited in that it will only support Read and Write access to one register at a time See the SMD Modbus Control Operation Manual section 2 for details and exceptions Data Master frame size 4 bytes 2 bytes for register number 2 bytes for either number of register to read or data to be written Slave frame size 3 or 4 bytes 3 bytes for read response data size in byte followed by the actual data there is an exception to this which is detailed in the SMD Modbus RTU Operations Manual 4 bytes for a write response which is a repeat of the original master data that was written Error Check The Error checking field is the result of a Cyclical Redundancy Checking CRC calculation that is performed on the message contents For full details on how to calculate the CRC please refer to the official Modbus RTU specification e Lenze Lenze DS041 AC Tech Q 4 _ O E L D j Modbus Registers The SMD Modbus Control Operation Manual provides a complete list
3. Getting Started with SMD amp Modbus RTU Communications Overview Modbus is an internationally accepted asynchronous serial protocol designed for commercial and industrial automation Modbus RTU is an RS485 based master slave system that can operate over a selected range of baud rates It was Developed by Modicon for PLC communications but today is also commonly used for basic parameter control on drives All L variant SMD drives have an integrated RS485 serial communication port and can fully support communication from a Modbus RTU master device such as a PC HMI or PLC Example part number of an L variant SMD drive ESMD371L2YXA Scope This document is intended to provide a helpful getting started guide for configuring the Modbus RTU masier to correctly communicate with a SMD drive and Is aimed to accompany the SMD Modbus RTU Operations Manual It is assumed that the user has familiarised themselves with how to navigate through the drive parameters using the keypad Refer to the drive user manual for details Methods for configuring master devices can differ greatly between manufacturers therefore details for configuring a specific network master are NOT provided herein However a very basic generic guide is provided Serial Port Parameters For devices that communicate on a Modbus serial network using the RTU Remote Terminal Unit mode it is possible to configure the master and slave serial ports in several different wa
4. of many of which have a direct relationship to actual drive parameters For every drive parameter there is a corresponding Modbus register However in addition to these there also several additional registers that are only accessible through Modbus All of these registers are detailed in the SMD Modbus Control Operation Manual To help clarify the statement in SMD Modbus Control Operation Manual section 2C Due to the way in which most Modbus masters typically access slave registers it may be necessary to add 1 to the SMD register number to ensure access to the correct register because the master automatically deducts 1 from the register number e g C37 Fixed setpoint is listed as register address 74 for SMD PV507 To correctly access this address the master actually needs to use register 40075 thereafter the master automatically deducts 1 during its message frame construction and will therefore really access drive register 40074 Some Modbus Master devices have the option to use zero base addressing de selecting this will simply everything as all registers will then have the correct off set i e 1 to 1 register addressing Drive Security For read access no security has to be set as read only access is always granted while C01 8 11 Assuming that the drive password has not been activated see C94 writing a value of 0 to drive register 48 40048 will unlock both drive control and parame
5. ter access lf a password has been configured then writing the password number to drive register 48 will again unlock access to both areas Writing only O to drive register 48 after a password has been configured will then only unlock access to the drive control registers Parameter access can be unlocked independently by writing 0 to drive register 49 To re activate re secure access to these areas simply set BIT 1 of the drive control register 1 Examples Example 1 Reading Fixed Setpoint 1 C37 default value of 20 Address Function Code Reg 01 03 00 4A Modbus Master request frame transmission Address Function Code Data Size Data Value 01 03 02 010E 075 Modbus Slave response frame transmission aa 00 _ 01 A5 DC Lenze Lenze DS041 AC Tech 4 _ O E L D j Example 2 Writing to a value of 12 3Hz to Fixed Setpoint 1 C37 Modbus Master request frame transmission N o Modbus Slave response frame transmission cen Ul Example 3 unlock security enable drive and control the motor speed The following drive parameters are assumed to have been already set e C01 11 default value is 0 e C09 1 as per default C94 0 as per default Close terminal 20 and 28 Function Code 06 Function Code 06 1 Unlocking security set a value of 0 to drive register 48 Modbus Master frame transmission ne Function Code 0 06
6. ys In order for communication to work correctly all devices on the network must be configured the same i e Baud rate Start bits Data size Parity Stop bits Drive Configuration Set the following drive parameters C01 Control Source Must be set to a value of 8 to 11 see the drive Operating Instructions for full details c25 Baud Rate This parameter actually configures more than just the drive baud rat it also configures all of the serial parameters as described above see the drive Operating Instructions for full details e n22 and n23 Serial Fault and time out see the drive Operating Instructions for full details Lenze Lenze DS041 AC Tech 4 _ O E L D j Modbus frame structure The message structure for a Modbus message is as follows Address Size 1 byte Valid slave nodes addresses are in the range of 0 247 decimal however address 0 is reserved for use as a broadcast address The individual slave devices are assigned addresses in the range of 1 247 each slave node on the network must have an individual address if two of more nodes have duplicate addresses this may prevent the network from functioning correctly A master addresses a slave by placing the slave address in the address field of the message When the slave returns its response it places its own address in the response address field to let the master know which slave is responding
Download Pdf Manuals
Related Search