MODBUS_SLAVE_B (197)

MODBUS_SLAVE_B (197)

ID                                                 197

Group: I/O

Short description:

Function that exchanges the indicated registers via the modbus protocol with the selected master device on the RS485 bus.

Inputs (5):

Outputs (3):

Settings: none

Description:

The MODBUS_SLAVE_B function communicates with external devices via the Modbus protocol. There are 6 functions in the block that can be used to send or receive data.

Function 06 - WriteSingleRegister enables writing a single register to the slave device, the number of registers in this case will always be equal to 1. The block can operate in two configurations. The first is to impulse the block. If 1 appears at the input of the block, the data from the modbus buffers will be copied once to the registers / markers. In this case, the master device may send data to the slave device, but does not have to. The above configuration synchronizes the data exchange from the slave device level. The second configuration is to set 1 to the block input permanently. At the moment of switching on the block, the block goes into the mode of waiting for data from the master. After receiving data from the master, the block copies the modbus buffers to the selected registers / markers. The next data exchange will take place only after receiving data from the master device. The above configuration synchronizes the data exchange with the master device.

Function 16 - WriteMultipleRegisters it is intended to send any number of registers. The block can operate in two configurations. The first is to impulse the block. If 1 appears at the input of the block, the data from the modbus buffers will be copied once to the registers / markers. In this case, the master device may send data to the slave device, but does not have to. The above configuration synchronizes the data exchange from the slave device level. The second configuration is to set 1 to the block input permanently. At the moment of switching on the block, the block goes into the mode of waiting for data from the master. After receiving data from the master, the block copies the modbus buffers to the selected registers / markers. The next data exchange will take place only after receiving data from the master device. The above configuration synchronizes the data exchange with the master device.

Function 03 - ReadHoldingRegisters  reads any registers of the slave device. The block can operate in two configurations. The first is to impulse the block. If 1 appears at the input of the block, then the defined registers / markers will be copied to the modbus buffers once. The master device can read this data at any time, but does not have to. If another pulse appears at the input of the block, the registers will be reloaded into the modbus buffers. The above configuration synchronizes the data exchange from the slave device level. The second configuration is to set 1 to the block input permanently. When the block is turned on, the registers / markers are copied once to the modbus buffers. The master device must receive the data for the block to reload the registers / markers. When the data is received by the master device, the registers / markers are automatically loaded into the modbus buffers. The above configuration synchronizes the data exchange with the master device. 

Function 01 - ReadCoils reads multiple markers from the slave device. The block can operate in two configurations. The first is to impulse the block. If 1 appears at the input of the block, then the defined registers / markers will be copied to the modbus buffers once. The master device can read this data at any time, but does not have to. If another pulse appears at the input of the block, the registers will be reloaded into the modbus buffers. The above configuration synchronizes the data exchange from the slave device level. The second configuration is to set 1 to the block input permanently. When the block is turned on, the registers / markers are copied once to the modbus buffers. The master device must receive the data for the block to reload the registers / markers. When the data is received by the master device, the registers / markers are automatically loaded into the modbus buffers. The above configuration synchronizes the data exchange with the master device.

Function 05 - WriteSingleCoil writes a single marker to the controller. The block can operate in two configurations. The first is to impulse the block. If 1 appears at the input of the block, the data from the modbus buffers will be copied once to the registers / markers. In this case, the master device may send data to the slave device, but does not have to. The above configuration synchronizes the data exchange from the slave device level. The second configuration is to set 1 to the block input permanently. At the moment of switching on the block, the block goes into the mode of waiting for data from the master. After receiving data from the master, the block copies the modbus buffers to the selected registers / markers. The next data exchange will take place only after receiving data from the master device. The above configuration synchronizes the data exchange with the master device.

Function 15 - WriteMultipleCoils writes multiple markers to the controller. The block can operate in two configurations. The first is to impulse the block. If 1 appears at the input of the block, the data from the modbus buffers will be copied once to the registers / markers. In this case, the master device may send data to the slave device, but does not have to. The above configuration synchronizes the data exchange from the slave device level. The second configuration is to set 1 to the block input permanently. At the moment of switching on the block, the block goes into the mode of waiting for data from the master. After receiving data from the master, the block copies the modbus buffers to the selected registers / markers. The next data exchange will take place only after receiving data from the master device. The above configuration synchronizes the data exchange with the master device.

During the communication, the busy output is turned on. The error and err_id outputs are activated when errors occur. The table style="width:100%" class="table table-bordered" with the description of the errors is presented below:

Notes:

• For the controller in version 4s2a, you can address from 1 to 127 slave devices
• In the 4s2a version of the controller, the functions intended for the management of inputs / outputs operate only on the markers
• In the 4s2a version of the controller, the permissible range of modbus addresses is from 0 to 999
• In the 4s2a version of the controller, the permissible range of controller register addresses is from 1 to 5000
• In the 4s2a version of the controller, the permissible range of controller marker addresses is from 1 to 2000
• In the 4s2a version of the controller, the maximum number of controller registers / markers and modbus registers is 800
• the minimum response time of the controller is about 30ms

R registers and M markers used:

The block uses user-defined registers or markers on the block inputs.