How to configure Read_var instruction to read 4x registers from Modbus server using Unity Premium Processor.

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Goals and Symptoms

This resolution is intended to be used as a guide to demonstrate how to configure the read_var instruction to read 4x (%MW) registers from Modbus server over a RS485 Network.

Facts and Changes

This example uses a TSXSCP114 RS485 communication card installed in channel 1 of the TSXP57104 processor. The Modbus server is a TSX Micro PLC with the TER port configured for Modbus server address 1.

Hardware

hardware
TSXP57104M Unity Processor
TSXSCP114 PCMCIA communication card.
TSXPACC01 RS485 Tap Link box
TSX372100 Micro PLC (Modbus Server device)

Operation and Debug

1, Create an animation table, enter the variables below. Click the Modification button. select the value for %M1. Click the up arrow to force the vale high.
This will initiate the Read_var instruction. Turn the block off with the down arrow.

table

Debugging

Management parameters:
%MW 10 - contains the Exchange number. This will change to an even number upon completion.
%MW11 - Should be viewed in Hex High byte - Operation Report, Low Byte - Communication Report
%MW12 - Time Out in 100ms
%MW13 - Length of data received

When on-line with the controller it is possible to see all slave devices connected to the Channel from the debug screen.

Upon each operation the COM LED will flash on the TSXSCP114 card.
The TER LED will also Flash on TSX Micro each time it is polled.

Attachments

The zip file below contains both Unity and PL7 programs.

Configuration

1 Create a new project using Premium processor of your choice.
2. Open the configuration screen, right click on the lower com port 'B' and select 'New/Replace Submodule'.
3. Select the 'TSXSCP114', click OK.
4. Double click Com port B on the processor, then highlight Channel 1, change the function to 'Modbus Jbus link' via drop down menu.
5. Change parity to None(If required), and validate the configuration.
6. Create a new FBD section within the Master Task.
7. From the toolbar select 'tools > project settings. Click the Language extension Tab and check the 'Directly represented Array variables' and 'Allow Dynamic arrays' (as detailed below) then click OK.
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8. Right click on the FBD screen and select FFB Input assistant.
9. Click on the FFB Browse button, Click on the Libset icon then select the Read_var. Click OK.
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10. This will then launch the Input Assistant. Enter details as required.
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The address configuration above comprised of the following syntax ADDR('Rack, Module, Channel, Slave address')
Rack = 0
Module = 0 - Processor, May also be 1 if a double wide power supply is used.
Channel = 1 - 0 for TER, 1 for PCMCIA port.
Slave = 1 - Modbus address of slave
Reads 50 consecutive registers starting at address %MW256 (40255) from slave at address 1.
The data is received into an array 50 registers starting at %MW100.
Transaction management parameters are an array 4 words starting at %MW10.
11. Click OK and place the Function block within the FBD section.
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12. The read_var block will be enabled from the output from a AND_BOOL function block. Launch the FFB Input assistant as before and select AND_BOOL from the Base Lib >Logic library, click OK.
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13. Complete Entry field details.
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The activity bit (%MW10.0) for the exchange is used prevent communication buffer overflow.
14. Click OK and place the Function block within the FBD section.
15. Negate Input %MW10.0 and connect the output from the AND_BOOL to the enable pin of the Read_var.
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16.Build the project and download to the controller.
17. Configure the Modbus slave set com parameters and speed to match the TSXSCP114. Set slave address to 1.
18. Download to the controller.

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Details above for TSX Micro TER Port (Channel 0)