Macro Guide 4: Using Free Protocol to Control a Device

Use the Free Protocol to Control a Device

If EasyBuilder Pro does not provide a driver for a specific device, users can use OUTPORT and INPORT built-in functions to control the device. The data sent by OUTPORT and INPORT must follow the communication protocol of the device. The following example explains how to use these two functions to control a MODBUS RTU device.

First, create a new device in the device table. The device type of the new device is set to “Free Protocol” and named with “MODBUS RTU device” as follows:

EBPro System Parameters, Device tab. Click 'New Device' and 'Free Protocol' as device type.

The interface of the device (I/F) uses [RS-232]. If a MODBUS TCP/IP device is connected, the interface should be [Ethernet] with correct IP and port number as follows:

I/F dropdown for Free Protocol device type can change between RS232/485/422/Ethernet. The Interface should match the device you are connecting.

Suppose that the HMI will read the data of 4x_1 and 4x_2 on the device. First, utilize OUTPORT to send out a read request to the device. The format of OUTPORT is:

OUTPORT(command[start], device_name, cmd_count)

Since “MODBUS RTU device” is a MODBUS RTU device, the read request must follow MODBUS RTU protocol. The request uses “Reading Holding Registers (0x03)” command to read data. The following picture displays the content of the command. (The items of the station number (byte 0) and the last two bytes (CRC) are ignored).

MODBUS Function table showing the content of the "0x03" command: read holding registers.

Depending on the protocol, the content of a read command as follows (The total is 8 bytes):

command[0]: station number (BYTE 0)
command[1]: function code (BYTE 1)
command[2]: high byte of starting address (BYTE 2)
command[3]: low byte of starting address (BYTE 3)
command[4]: high byte of quantity of registers (BYTE 4)
command[5]: low byte of quantity of registers (BYTE 5)
command[6]: low byte of 16-bit CRC (BYTE 6)
command[7]: high byte of 16-bit CRC (BYTE 7)

So a read request is designed as follows:

Read Request Command within a macro example. This is simply for a read request itself, as there is no actual Device references yet.

Lastly, use OUPORT to send out this read request to the device.

OUTPORT command: This is the one that takes the read request and sends it to the device.

After sending out the request, use INPORT to get the response from the device. Depending on the protocol, the content of the response is as follows (the total byte is 9):

response[0]: station number (BYTE 0)
response[1]: function code (BYTE 1)
response[2]: byte count (BYTE 2)
response[3]: high byte of 4x_1 (BYTE 3)
response[4]: low byte of 4x_1 (BYTE 4)
response[5]: high byte of 4x_2 (BYTE 5)
response[6]: high byte of 4x_2 (BYTE 6)
response[7]: low byte of 16-bit CRC (BYTE 7)
response[8]: high byte of 16-bit CRC (BYTE 8)

The format of INPORT is:

INPORT command format is the command that reads the device's response.

Where the real read count is restored to the variable return_value (unit is byte). If return_value is 0, it means reading fails in executing INPORT.

According to the MODBUS RTU protocol specification, the correct response[1] must be equal to 0x03. After getting correct response, calculate the data of 4x_1 and 4x_2 and put in the data into LW-100 and LW-101 of HMI.

Macro sample takes the data of the MODBUS addresses and puts it into local HMI memory after getting the correct response.

The complete macro is as follows:

Complete macro to read holding registers and then transfer data to local HMI memory

The following example explains how to design a request to set the status of 0x_1. The request uses ”Write Single Coil(0x5)” command.

MODBUS Function table showing the content of the "0x5" command: write single coil.

The complete macro is as follows:

Complete macro with the write single coil command. The status of Modbus Address 0X:1 is set at the completion of the macro sequence.