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--- en:sw:01-mervis:connecting-to-modbus-slave-device-hidden [2018/06/19 07:06]
martin_kudlacek [Connecting to ModbusRTU slave]
+++ en:sw:01-mervis:connecting-to-modbus-slave-device-hidden [2021/08/05 12:25] (current)
avsetula
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 ====== Connecting to Modbus slave ======
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 One of the most common thing todo in industrial automation, is setting up the communication via Modbus.
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+<html><span class="dev-tag dev-patron">Patron</span></html> \\
+<html><span class="dev-tag dev-neuron">Neuron</span></html> \\
+<html><span class="dev-tag dev-gate">Gate</span></html> \\
+<html><span class="dev-tag dev-unipi11">Unipi&nbsp1.1</span></html> \\
+<html><span class="dev-tag dev-axon">Axon</span></html>
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 ===== Connecting to ModbusRTU slave =====
 Let's assume you have a basic project in **Full mode**. You are attached to the controller, you have created **Executable project** with one **FBD** program and this program is set in PLC's **Tasks**. You also did a **Set Autogen** on the UniPi controller, and the **Build** and **Deploy** works without any problem.
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 </WRAP>
+===== Configuration of datapoints =====
 The basic configuration of the ModbusRTU device is done, now we can dive into much more complicated stuff - the register map. Double click on the name of the newly added device. In the **Main window** an empty list of Modbus registers will appear.
 {{ :en:sw:01-mervis:connecting-to-modbus-slave-09-modbus-register-map.png?direct |}}
-The values in Modbus slave devices are "shared" via registers (a strictly 16bit values) or coils (strictly 1bit statuses). In order to acquire these values from the slaves, we need to define, which registers we want to read and possibly, how to transform them into variables, which we can later use in our program.
+The values in Modbus slave devices are "shared" via registers (a strictly 16 bit values) or coils (strictly 1 bit statuses). In order to acquire these values from the slaves, we need to define, which registers we want to read and possibly, how to transform them into variables, which we can later use in our program.
 It is time to introduce our ModbusRTU device, from which we want to read the data: The Inepro PRO1-Mod energy meter.
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 Unfortunately, this is where it starts to be really complicated, mostly due to the various ways of how the Modbus protocol is implemented by different vendors.
-As you can see, the register's addresses are in hexadecimal format. You can't tell from the **Voltage** register, because the address of 5000 could be both in hexadecimal and decimal format. But if you take a look on the **Current** register, the value 500A clearly shows it is in hexadecimal format.
+As you can see, the register's addresses are in hexadecimal format. You can't tell from the **Voltage** register, because the address of 5000 could be both in hexadecimal and decimal format. But if you take a look on the **Current** register, the value 500 A clearly shows it is in hexadecimal format.
 The Mervis IDE accepts only decimal values for Modbus registers, so you need to manually convert the ones from the manual, e.g. with calculator application in Windows or in MS Excel.
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 {{ :en:sw:01-mervis:connecting-to-modbus-slave-10-add-group.png?direct |}}
-A new group called **Group** will appear and also three other **datapoints** were created. Click on the row with name **Group** and in the **Properties panel**, change the **Name** to something more descriptive. We picked the range of original addresses according to the manual (5000 - 5000B). In the **Modbus Group Parameters** we need to specify the number of the first register, or as it is called here **Starting Element**. As we calculated above, the **Starting Element** for register **Voltage** is 20481. The Modbus function is **F03 Read Holding Registers**. The **Quantity of Elements** is a number of registers we want to read from the slave device into this group for later processing into datapoints. Select 12, because we want to read the **Voltage**, **Grid frequency** and **Current** at once.
+A new group called **Group** will appear and also three other **datapoints** were created. Click on the row with name **Group** and in the **Properties panel**, change the **Name** to something more descriptive. We picked the range of original addresses according to the manual (5000-5000B). In the **Modbus Group Parameters** we need to specify the number of the first register, or as it is called here **Starting Element**. As we calculated above, the **Starting Element** for register **Voltage** is 20481. The Modbus function is **F03 Read Holding Registers**. The **Quantity of Elements** is a number of registers we want to read from the slave device into this group for later processing into datapoints. Select 12, because we want to read the **Voltage**, **Grid frequency** and **Current** at once.
 {{ :en:sw:01-mervis:connecting-to-modbus-slave-12-group-for-voltage.png?direct |}}
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 {{ :en:sw:01-mervis:connecting-to-modbus-slave-21-variable-browser.png?direct |}}
+To be able to continue with the tutorial, you need to fully understand, what we did with the **Voltage** and how to represent different data types in Modbus.
+The Modbus knows only 16 bit registers (forget about the "coils" for now). Therefor in one register, we can store only 65536 values. Those values can represent different types of numbers. It can represent unsigned integer number from 0-65535. It can represent signed integer from -32768 to 32767. Or we don't need to use all the possible values and covert it directly to "char" number with values 0-255.
+But if you need to exchange data type with slave, which needs more then 16 bit of space, you need to use more than 1 Modbus register and then do the transformation of data in the Mervis. This is what we did with the **Voltage**. The **Voltage** is a real number which needs 32 bit space. In the Inepro manual, you can see the data type is "float" and the register's length is 2. This doesn't mean the register has different size other than 16 bit, but rather tells us the **Voltage** is stored in 2 registers - on address 5000H and 5001H. In order to recreate the value in Mervis, we had to read 2 registers and put them together into one variable.
+This parsing of multiple registers into datapoint (variable) is done on two levels. First, we need to tell the Mervis to read more registers at once. This is done on the **Group** level. We specified **the first register number** we want to read (the **Starting Element**) and the number of registers we want to read from this number (the **Quantity of Elements**). As you can check above, we started reading from the register number 20481 and we read 12 consecutive 16 bit registers = 24 bytes.
+Next thing we did, is that we specified the **Voltage** datapoint. We pointed this datapoint to the group, so it will be taking data from this group and transform it to some variable. To tell exactly, which data from the group the datapoint should use, we configured the **Modbus Data Point Parameters**. For reading data from group to datapoint, you need to set the **Data Offset (Parser)** and the **Multibyte Length (Parser)**.
+The **Data Offset (Parser)** indicates the first **byte** (not register!) from the group, and the **Multibyte Length (Parser)** is a number of **bytes** to parse into this variable. As you can check, we selected first 4 bytes from the group (Data Offset = 0, Multibyte Length = 4), which corresponds with 2 registers (4*8 bit = 2*16 bit). And by setting the **ST Type**, we set the transformation of this 32 bit data space into a real number. It sounds a quite complicated, but with next datapoint, it will be a bit clearer hopefully.
+So let's add another datapoint - **Grid frequency**. As you can see from the Modbus register's map, the **Grid frequency** is on the address 5008 and the register's length (more like value length) is 2. We know, we already have the group **5000-500B** configured to cover these registers as well, therefor we can define the datapoint directly. Right click on the free space on the tab **energyMeterL1** on the **Main window** and from the context menu select **Add Data Point**. A new datapoint will appear and you can change its properties. The result should look like this:
+{{ :en:sw:01-mervis:connecting-to-modbus-slave-22-grid-frequency.png?direct |}}
+  * We named the datapoint **GridFrequency**
+  * We specified to take data from group **5000-500B**
+  * The **Comm. Value Mapped Type** is **Builtin** and the **ST Type** is **real**
+  * The **Data Offset (Parser)** = (address of the register - address of the first register in group) * 2 = (5008H-5000H) * 2 = 16
+  * The **MultiByte Length (Parser)** is 4 (4 bytes = 2 16 bit registers)
+Because we added new datapoint, you need to run the **Set Autogen** on the device. Then **Deploy** the solution, turn on the **Debugging** mode and switch to **Variable Browser** tab in **Main window**. In the browser, search for the **energyMeterL1**. You should see this:
+{{ :en:sw:01-mervis:connecting-to-modbus-slave-23-variable-browser.png?direct |}}