12Lf Series ModbusRTU Manual

1 Introduction

The MODBUS is an industrial protocol and is a standard protocol mainly used for PLC communication. MODBUS has several different types - RTU, ASCII, and recently TCP method, and we have applied MODBUS RTU for our actuators.

The industry's de facto serial standard since 1979, MODBUS has enabled millions of automation devices to communicate stably & safely. MODBUS is a request/response protocol and provides services specified by function code. The frame consists of ADU, which is an Application Data Unit, and PDU, which stands for Protocol Data Unit

2 Frame Structure

2.1 Packet Description

The mightyZAP complies with the standard MODBUS-RTU protocol. For the detailed MODBUS RTU specification not covered in this manual, please refer to the MODBUS official website. [https://www.modbus.org/specs.php].

2.1.1 Packet Structure

The maximum transmit/receive packet length of the MODBUS-RTU protocol is 256 Bytes. Therefore, please be careful that the total length of the TX/RX packets does not exceed 256 bytes. MODBUS-RTU communication mode requires an empty space of at least 3.5 Char between the Start and End to distinguish packets as shown in the figure below .

• Transmit Packet Structure

	Address	Fucntion code	Data			Error Check
byte	0	1	2			n-1	n
Data	mightyZAP ID	Function	Data			CRC(MSB)	CRC(LSB)

• Receive Packet Structure - Normal Response

	Address	Fucntion code	Data			Error Check
byte	0	1	2			n-1	n
Data	mightyZAP ID	Function	Data			CRC(MSB)	CRC(LSB)

• Receive Packet Structure - Abnormal Response

	Address	Fucntion code	Data	Error Check
byte	0	1	2	3	4
Data	mightyZAP ID	Function + 0x80	Exception code	CRC(MSB)	CRC(LSB)

2.1.2 Packet Element Description

2.1.2.1 Start

• This refers to the minimum time to distinguish between different frames.
• At a communication speed of 57600bps, the transmission time for 1 bit is 0.017msec, and since the start time is 3.5 character time (1 character = 8bit), the minimum start time is 0.486msec.
• If a frame shorter than the minimum start time is transmitted, it is recognized as continuous data from the previous frame.

2.1.2.2 Address

• mightyZAP's ID. An identifier to support Serial daisy chain connection in a multi-connection method.
• With the ID '0', it operates as Broadcasting ID.

2.1.2.3 Function Code

• The MODBUS-RTU standard function code supported by mightyZAP is as follows.

Function	Code	Description
Read Holding Register	0x03	Reading data from mightyZAP
Write Single Register	0x06	Setting data value in a specific address of mightyZAP
Write Multiple Register	0x10	Setting data values ​​in consecutive addresses of mightyZAP

2.1.2.4 Data

Transmission

• In the case of the Read Register command, the MODBUS address, number of registers, number of bytes, etc. are specified, and in the case of the Write Register command, the MODBUS address, number of bytes, value to be set, etc. are specified.

Reception

• In the case of the Read Register command, the normal response is that the Node ID and Function Code are received with the same values ​​as when transmitted, and the data is received as the value of each register according to the order of the registers sent during transmission.
• In the case of the Write Single Register command, the same data as transmitted is received. In the case of Write Multi Register, the starting address and number of registers for which data is to be written are received with the Write Multi Register command.
• In the case of an abnormal response, it consists of Node ID, Error Code, and Exception Code, and the packet structure of the abnormal response is the same regardless of the function code.
• In the case of an abnormal response, it consists of Node ID, Error Code, and Exception Code, and the packet structure of the abnormal response is the same regardless of the function code.

2.1.2.5 CRC

• Enter a 16-bit CRC value and it consists of 2 bytes.
• The transmission order is lower 1 byte, upper 1 byte.
• CRC Check Method is CRC-16(X^16 + X^15+X^2+1). For easier calculation, get CRC-16 MODBUS calculator on the Internet.

2.1.2.6 Exception Code

• Exception codes for abnormal responses to all function codes supported by mightyZAP are defined as follows.

Exception Code		Description
0x01	Illegal Function	Function code which are not supported
0x02	Illegal Data Address	Invalid register address
0x03	Illegal Data Value	Invalid data value
0x04	Slave Device Failure	Device failure, parameter setting value error (ready)
0x05	Acknowledge	Data is not ready (ready)
0x06	Slave Device Busy	Parameter lock status

2.2 Protocol Function Code Description

2.2.1 Read Holding Register (0x03)

Reads the values ​​of a single register (16-bit data) and consecutive register blocks (16-bit data units).

2.2.1.1 Packet Description

	Address	Fucntion code	Starting Address	Quantity of Register	CRC
Size(byte)	1 byte	1 byte	2 byte	2 byte	2 byte
Data		0x03	0x0000 to 0xffff	1 to 125(0x7d)

	Address	Fucntion code	Byte Count	Register Value	CRC
Size(byte)	1 byte	1 byte	1 byte	N* x 2 bytes	2 byte
Data		0x03	2 x N*
*N = Quantity of Registers

	Address	Error code	Exception Code	CRC
Size(byte)	1 byte	1 byte	1 byte	2 byte
Data		0x83	0x01 to 0x06

2.2.1.2 Frame Detail

• Address
  Unique ID of mightyZAP from which user wants to read data.
• Function Code Code 0x03, meaning Read Holding Register command
• Starting Address Starting address of the data which user wants to read and it consists of 2 bytes.
• Quantity of Register Size of the data to be read and it consists of 2 bytes.
• CRC It uses the CRC error check method and consists of 2 bytes.
• Byte Count Number of responding data.
• Register Value Data is transmitted in byte units using the address of the request frame as the starting address. Since the data is a WORD type, the size is the same as doubling the number of bytes.
• Error code The error code is expressed by adding the value 80 (Hex) to the function code. In the case of the Read Holding register, it is transmitted as 83 (Hex).
• Exception code Detailed error details and it consists of 1 byte.

2.2.1.3 Example

#1 - Read Present Position (0xD2)

• Request

Address	Fucntion code	Starting Address Hi	Starting Address Lo	Quantity of Register Hi	Quantity of Register Lo	CRC Lo	CRC hi
0x01	0x03	0x00	0xD2	0x00	0x01	0x24	0x33

• Request OK -Present Position Data :1000

Address	Fucntion code	Byte Count	Register value Hi	Register value Lo	CRC Lo	CRC hi
0x01	0x03	0x02	0x03	0xe8	0xB8	0xFA

• Request Not OK

Address	Error code	Exception Code	CRC Lo	CRC hi
0x01	0x83	0x04	CRC Lo	CRC hi

#2 - Read Present Current (0xD3)

• Request

Address	Fucntion code	Starting Address Hi	Starting Address Lo	Quantity of Register Hi	Quantity of Register Lo	CRC Lo	CRC hi
0x01	0x03	0x00	0xD3	0x00	0x01	0x75	0xf3

• Request OK -Present Current Data : 426

Address	Fucntion code	Byte Count	Register value Hi	Register value Lo	CRC Lo	CRC hi
0x01	0x03	0x02	0x01	0xAA	0x39	0xAB

• Request Not OK

Address	Error code	Exception Code	CRC Lo	CRC hi
0x01	0x83	0x04	0x40	0xF3

2.2.2 Write Single Register

Writes a value to a single register (16-bit data).

2.2.2.1 Packet Description

	Address	Fucntion code	Register Addresse	Register Value	CRC
Size(byte)	1 byte	1 byte	2 byte	2 byte	2 byte
Data		0x06	0x0000 to 0xffff	0x0000 to 0xffff

	Address	Fucntion code	Register Addresse	Register Value	CRC
Size(byte)	1 byte	1 byte	2 byte	2 byte	2 byte
Data		0x06	0x0000 to 0xffff	0x0000 to 0xffff

*N = Quantity of Registers

	Address	Error code	Exception Code	CRC
Size(byte)	1 byte	1 byte	1 byte	2 byte
Data		0x86	0x01 to 0x06

2.2.2.2 Frame Detail

• Address Unique ID of mightyZAP where the user wants to write data.
• Function Code Code 0x06, meaning Write Single Register command.
• Register Address Address of the data user wants to write and it consists of 2 bytes.
• Register Value Data value user wants to write and it consists of 2 bytes.
• CRC It uses the CRC error check method and consists of 2 bytes.
• Error code The error code is expressed by adding the value 80 (Hex) to the function code, and in the case of the Read Holding register, it is transmitted as 83 (Hex).
• Exception code Detailed error details and it consists of 1 byte.

2.2.2.2 Example

#1 - Write Goal Position (0xCD)

• Request - Goal Position Data : 1000

Address	Fucntion code	Register Address Hi	Register Address Lo	Register Value Hi	Register Value Lo	CRC Lo	CRC hi
0x01	0x06	0x00	0xCD	0x03	0xE8	0x18	0x8B

• Request OK

Address	Fucntion code	Register Address Hi	Register Address Lo	Register Value Hi	Register Value Lo	CRC Lo	CRC hi
0x01	0x06	0x00	0xCD	0x03	0xE8	0x18	0x8B

• Request Not OK

Address	Error code	Exception Code	CRC Lo	CRC hi
0x01	0x86	0x04	CRC Lo	CRC hi

#2 - Write Goal Current (0xD3)

• Request - Goal Current Data : 800

Address	Fucntion code	Register Address Hi	Register Address Lo	Register Value Hi	Register Value Lo	CRC Lo	CRC hi
0x01	0x06	0x00	0xD1	0x03	0x20	0xD8	0xDB

• Request OK

Address	Fucntion code	Starting Address Hi	Starting Address Lo	Quantity of Register Hi	Quantity of Register Lo	CRC Lo	CRC hi
0x01	0x06	0x00	0xD1	0x03	0x20	0xD8	0xDB

• Request Not OK

Address	Error code	Exception Code	CRC Lo	CRC hi
0x01	0x86	0x04	0x40	0xF3

2.2.3 Write Multi Register(0x10)

Writes values ​​to consecutive register blocks (16-bit data units).

2.2.3.1 Packet Description

	Address	Fucntion code	Starting Address	Quantity of Register	Byte Count	Registers Value	CRC
Size(byte)	1 byte	1 byte	2 bytes	2 bytes	1Byte	N* x 2 Bytes	2 byte
Data		0x10	0x0000 to 0xffff	0x0000 to 1 to 0x007B(123)	2 x N*	value

	Address	Fucntion code	Starting Address	Quantity of Register	CRC
Size(byte)	1 byte	1 byte	2 bytes	2 bytes	2 byte
Data		0x10	0x0000 to 0xffff	0x0000 to 1 to 0x007B(123)

*N = Quantity of Registers

	Address	Error code	Exception Code	CRC
Size(byte)	1 byte	1 byte	1 byte	2 byte
Data		0x90	0x01 to 0x06

2.2.3.2 Frame Detail

• Address The unique ID of mightyZAP which user wants to write data.
• Function Code Code 0x10, meaning Write Multi Register command
• Start Addresse Starting address of the data user wants to write in succession and it consists of 2 bytes.
• Quantity of Register Size of data user wants to write and it consists of 2 bytes.
• Byte Count Number of data user wants to write in succession.
• Registers Value A set of 2 bytes as the value of the data user wants to write. Must add as many data sets as user entered in Byte Count.
• CRC It uses the CRC error check method and consists of 2 bytes.
• Error code The error code is expressed by adding 80 (Hex) to the function code, and in the case of the read holding register, it is transmitted as 0x90.
• Exception code Detailed error details and it consists of 1 byte.

2.2.3.3 Example

#1 - Multi Write Goal Speed(0xD0) & Goal Current (0xD1)

• Request - Goal Speed Data : 1000, Goal Current Data : 800

Address	Fucntion code	Starting Address Hi	Starting Address Lo	Quatity of Register Hi	Quatity of Register Lo	Byte Count	Register Value Hi	Register Value Lo	Register Value Hi	Register Value Lo	CRC Lo	CRC hi
0x01	0x10	0x00	0xD0	0x00	0x02	0x04	0x03	0xE8	0x03	0x20	0x7F	0xAB

• Request OK

Address	Fucntion code	Starting Address Hi	Starting Address Lo	Quatity of Register Hi	Quatity of Register Lo	CRC Lo	CRC hi
0x01	0x10	0x00	0xD0	0x00	0x02	0x40	0x31

• Request Not OK

Address	Error code	Exception Code	CRC Lo	CRC hi
0x01	0x83	0x04	0x40	0xF3

3. Packet Test