Advanced Serial Data Logger

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For Windows 2000 - Windows 10 (2019) (incl. Server, x86 and x64). Latest version: 4.4.3 build 911. .


SQL to MODBUS: Sending data from a SQL database to MODBUS

Problem scenario:

My goal is to write data from my database to PLC using MODBUS.

Requirements:

  • Data Logger Suite Enterprise or a trial version. This logger can work with MODBUS RTU and TCP at the same time.

It is assumed that:

You have configured the communication settings on the device:

  • MODBUS TCP - IP address, Subnet, Gateway. You must assign a static IP address for the device.
  • MODBUS RTU - baud rate and the number of data bits.

Solution:

1. Create a new configuration from the main window using the "Green Plus" button. (fig. 1). Usually, you need to select the "TCP/IP" interface type for MODBUS TCP and "RS232" for MODBUS RTU. This example shows the connection settings for MODBUS TCP. If your device uses MODBUS RTU, look here. If you've already configured the connection, then go to step #2.

IP connection settings
Fig. 1: IP connection settings

2. Go to the "Modules - Query Parser Filter" page. Select the "MODBUS TCP" or "MODBUS RTU" plugin from lists. Then click the "Setup" button.

MODBUS plugin selection
Fig. 2: Selecting the MODBUS plugin

3. Click "Action - Add request" and add new requests to write data (fig. 3-5).

3.1. Set the correct function code. The MODBUS function code should be:

  • 6 (Write single register) - if you need to write a value that allocated one MODBUS register in the PLC memory. For example, the value of the data type word, uint16, int16, decimal16.
  • 16 (Write multiple registers) - if you need to write larger values (dword, uint32, int32, decimal32, float, etc.).

3.2. The number of registers:

  • word, int16, unt16 - one MODBUS registers (2 bytes).
  • dword, int32, uint32, float - two registers (4 bytes).
  • int64, double precision float - four registers (8 bytes).

3.3. The MODBUS address does not matter. The plugin will receive it from a database.

3.4. Select the "Event" request method. Then specify the event identifier like "WRITE-INT," "WRITE-FLOAT," "WRITE-UINT16". You may use other identifiers but should change them in the next steps too.

Note: You should add a separate request with a different event ID for each data type. For example, one request writes "int" values, another one "float" values.

3.5. Add only one response item to each request with the "VALUE" name.

Adding the "Write" request
Fig. 3: Adding the "Write" request

Writing Int32
Fig. 4: Writing Int32

Writing Float
Fig. 5: Writing Float

4. Prepare a table in your SQL database. You may use the following prototypes. The table will contain one row for each register. The "DATE_TIME_STAMP" column specifies the time when the value is changed last time. The logger will use this column to read updates from the table.

Below you can find some table-creating scripts that we recommend to use.

CREATE TABLE [dbo].[MODBUS_DATA_WRITE](
	[ID] [decimal](10, 0) IDENTITY(1,1) NOT NULL,
	[DATE_TIME_STAMP] [datetime] NULL DEFAULT (getdate()),
	[DATA_SOURCE] [nvarchar](32) NOT NULL,
	[DEVICE_ID] [int] NOT NULL,
	[OFFSET] [int] NULL,
	[VALUE1] [int] NULL,
	[VALUE2] [float] NULL,
	[VALUE3] [smallint] NULL
 CONSTRAINT [PK_MODBUS_DATA_WRITE] PRIMARY KEY CLUSTERED 
(
	[ID] ASC
)WITH (IGNORE_DUP_KEY = OFF) ON [PRIMARY]
) ON [PRIMARY]

GO

CREATE TRIGGER dbo.MODBUS_DATA_WRITE_TRIGGER
ON dbo.MODBUS_DATA_WRITE
AFTER UPDATE 
AS BEGIN
   SET NOCOUNT ON
   UPDATE dbo.MODBUS_DATA_WRITE
   SET DATE_TIME_STAMP = GETDATE()
   FROM INSERTED
   WHERE INSERTED.ID = MODBUS_DATA_WRITE.ID
END
GO 

CREATE TABLE `MODBUS_DATA_WRITE` (
 `ID` int(11) NOT NULL auto_increment,
 `DATE_TIME_STAMP` DATETIME NULL,
 `DATA_SOURCE_NAME` VARCHAR(32) NOT NULL,
 `DEVICE_ID` INTEGER NOT NULL,
 `OFFSET` INTEGER NULL,
 `VALUE1` INTEGER NULL,
 `VALUE2` DOUBLE NULL,
 `VALUE3` INTEGER NULL,
  PRIMARY KEY  (`ID`)
) ENGINE=InnoDB;

CREATE TRIGGER MODBUS_DATA_WRITE_BI BEFORE INSERT ON `MODBUS_DATA_WRITE`
    FOR EACH ROW SET NEW.DATE_TIME_STAMP = IFNULL(NEW.DATE_TIME_STAMP, NOW());

CREATE TRIGGER MODBUS_DATA_WRITE_BU BEFORE UPDATE ON `MODBUS_DATA_WRITE`
    FOR EACH ROW SET NEW.DATE_TIME_STAMP = IFNULL(NEW.DATE_TIME_STAMP, NOW());

CREATE TABLE "MODBUS_DATA_WRITE" (
  "ID" SERIAL,
  "DATE_TIME_STAMP" timestamp DEFAULT NULL,
  "DATA_SOURCE_NAME" varchar(32) NOT NULL,
  "DEVICE_ID" integer NOT NULL,
  "OFFSET" integer NULL,
  "VALUE1" integer NULL,
  "VALUE2" real NULL,
  "VALUE3" integer NULL,
  PRIMARY KEY ("ID")
);

CREATE OR REPLACE FUNCTION MODBUS_DATA_WRITE_BI_TRIGGER()
  RETURNS trigger AS
$BODY$
BEGIN
 NEW.DATE_TIME_STAMP := COALESCE(NEW.DATE_TIME_STAMP, NOW());
 RETURN NEW;
END;
$BODY$ LANGUAGE plpgsql;

CREATE TRIGGER MODBUS_DATA_WRITE_BI BEFORE INSERT ON "MODBUS_DATA_WRITE"
    FOR EACH ROW EXECUTE PROCEDURE MODBUS_DATA_WRITE_BI_TRIGGER();

CREATE TRIGGER MODBUS_DATA_WRITE_BU BEFORE UPDATE ON "MODBUS_DATA_WRITE"
    FOR EACH ROW EXECUTE PROCEDURE MODBUS_DATA_WRITE_BI_TRIGGER();

5. Create a new configuration with SQL interface by clicking the "Green Plus" button in the main window.

Adding the SQL data source
Fig. 6: Adding the SQL data source

6. Configure connection with your database (page #100).

Database connection settings
Fig. 7: Database connection settings

7. Specify the name of your database table, the polling interval, and the "DATE_TIME_STAMP" field name.

Database table
Fig. 8: Database table

When the SQL interface reads data, it appears in the main window.

SQL data
Fig. 9: SQL data

8. Select the "OPC parser" plugin. This plugin does not have any settings.

Parser plugin
Fig. 10: Parser plugin

9. Script execute - this plugin executes a script and sends values from the database table to the necessary data source (an IP address or an RS232 port), a device, and an address.

Selecting the Script Execute plugin
Fig. 11: Script Execute plugin

10.Copy and paste the following script.

var
 device, addr: integer;
 v1, v2, v3: variant;
 strTargetDataSource: string;
begin
 strTargetDataSource := GetVariable('DATA_SOURCE');
 device := GetVariable('DEVICE_ID'); // MODBUS device ID
 addr := GetVariable('OFFSET'); // MODBUS memory offset
 v1 := GetVariable('VALUE1'); // Int value
 v2 := GetVariable('VALUE2'); // Float value
 v3 := GetVariable('VALUE3'); // UInt16 value

 if VarToStr(v1) <> '' then
   SendEventEx('WRITE-INT', [
   'EVENT-TO-CFG', strTargetDataSource,
   'DEVICE', device,
   'ADDRESS', addr,
   'VALUE', v1
  ]);

 if VarToStr(v2) <> '' then
   SendEventEx('WRITE-FLOAT', [
   'EVENT-TO-CFG', strTargetDataSource,
   'DEVICE', device,
   'ADDRESS', addr,
   'VALUE', v2
  ]);

 if VarToStr(v3) <> '' then
   SendEventEx('WRITE-UINT16', [
   'EVENT-TO-CFG', strTargetDataSource,
   'DEVICE', device,
   'ADDRESS', addr,
   'VALUE', v3
  ]);

end.

Script
Fig. 12: Script

11. Now, the application works in the following way:

  • The SQL interface reads data from a database table.
  • The "OPC parser" plugin prepares data for the "Script Execute" plugin.
  • The "Script Execute" plugin redirects SQL data to different data sources and devices using events.
  • The "MODBUS" plugin in another configuration handles an event, and execute the "write" request.

12. You may execute a SQL statement like the following and insert a new row to the table.


  INSERT INTO MODBUS_DATA_WRITE (DATA_SOURCE, DEVICE_ID, OFFSET, VALUE3) 
VALUES ('192.168.1.3:502', 1, 10, 14321)

You may download the backup copy of this configuration here and restore from the "File" menu in the main window.

Related articles:

MODBUS RTU, MODBUS ASCII, MODBUS/TCP

IEC 62056-21