Mitsubishi RJ71C24, RJ71C24-R2, RJ71C24-R4, RJ71EN71, R04ENCPU Reference Manual

MELSEC iQ-R MODBUS and MODBUS/TCP

Reference Manual

-RJ71C24 -RJ71C24-R2 -RJ71C24-R4 -RJ71EN71 -R04ENCPU -R08ENCPU -R16ENCPU -R32ENCPU -R120ENCPU

SAFETY PRECAUTIONS

(Read these precautions before using this product.)

Before using MELSEC iQ-R series programmable controllers, please read the manuals for the product and the relevant manuals introduced in those manuals carefully, and pay full attention to safety to handle the product correctly.

Make sure that the end users read this manual and then keep the manual in a safe place for future reference.

CONDITIONS OF USE FOR THE PRODUCT

(1)MELSEC programmable controller ("the PRODUCT") shall be used in conditions;

i)where any problem, fault or failure occurring in the PRODUCT, if any, shall not lead to any major or serious accident; and

ii)where the backup and fail-safe function are systematically or automatically provided outside of the PRODUCT for the case of any problem, fault or failure occurring in the PRODUCT.

(2)The PRODUCT has been designed and manufactured for the purpose of being used in general industries. MITSUBISHI ELECTRIC SHALL HAVE NO RESPONSIBILITY OR LIABILITY (INCLUDING, BUT NOT LIMITED TO ANY AND ALL RESPONSIBILITY OR LIABILITY BASED ON CONTRACT, WARRANTY, TORT, PRODUCT LIABILITY) FOR ANY INJURY OR DEATH TO PERSONS OR LOSS OR DAMAGE TO PROPERTY CAUSED BY the PRODUCT THAT ARE OPERATED OR USED IN APPLICATION NOT INTENDED OR EXCLUDED BY INSTRUCTIONS, PRECAUTIONS, OR WARNING CONTAINED IN MITSUBISHI ELECTRIC USER'S, INSTRUCTION AND/OR SAFETY MANUALS, TECHNICAL BULLETINS AND GUIDELINES FOR the PRODUCT.

("Prohibited Application")

Prohibited Applications include, but not limited to, the use of the PRODUCT in;

•Nuclear Power Plants and any other power plants operated by Power companies, and/or any other cases in which the public could be affected if any problem or fault occurs in the PRODUCT.

•Railway companies or Public service purposes, and/or any other cases in which establishment of a special quality assurance system is required by the Purchaser or End User.

•Aircraft or Aerospace, Medical applications, Train equipment, transport equipment such as Elevator and Escalator, Incineration and Fuel devices, Vehicles, Manned transportation, Equipment for Recreation and Amusement, and

Safety devices, handling of Nuclear or Hazardous Materials or Chemicals, Mining and Drilling, and/or other applications where there is a significant risk of injury to the public or property.

Notwithstanding the above restrictions, Mitsubishi Electric may in its sole discretion, authorize use of the PRODUCT in one or more of the Prohibited Applications, provided that the usage of the PRODUCT is limited only for the specific applications agreed to by Mitsubishi Electric and provided further that no special quality assurance or fail-safe, redundant or other safety features which exceed the general specifications of the PRODUCTs are required. For details, please contact the Mitsubishi Electric representative in your region.

(3)Mitsubishi Electric shall have no responsibility or liability for any problems involving programmable controller trouble and system trouble caused by DoS attacks, unauthorized access, computer viruses, and other cyberattacks.

1

INTRODUCTION

Thank you for purchasing the Mitsubishi Electric MELSEC iQ-R series programmable controllers.

This manual describes the frame specifications and MODBUS standard functions to use the MODBUS slave function and MODBUS/TCP slave function of the following modules.

Before using this product, please read this manual and the relevant manuals carefully and develop familiarity with the functions and performance of the MELSEC iQ-R series programmable controller to handle the product correctly.

Relevant products

RJ71C24, RJ71C24-R2, RJ71C24-R4

RJ71EN71, R04ENCPU, R08ENCPU, R16ENCPU, R32ENCPU, R120ENCPU

2

CONTENTS

SAFETY PRECAUTIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1 CONDITIONS OF USE FOR THE PRODUCT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1 INTRODUCTION. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2 RELEVANT MANUALS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5 TERMS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5 GENERIC TERMS AND ABBREVIATIONS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5

CHAPTER 1 FRAME SPECIFICATIONS

6

1.1 MODBUS Protocol Frame Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

RTU mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 ASCII mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

1.2 MODBUS/TCP Protocol Frame Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 1.3 Protocol Data Unit Formats Grouped by Function. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

CHAPTER 2	MODBUS STANDARD FUNCTION LIST	13
CHAPTER 3	MODBUS STANDARD FUNCTION DETAILS	14

3.1 Read Coils (FC: 01H). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 3.2 Read Discrete Inputs (FC: 02H) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 3.3 Read Holding Registers (FC: 03H) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 3.4 Read Input Registers (FC: 04H) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 3.5 Write Single Coil (FC: 05H) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 3.6 Write Single Register (FC: 06H) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 3.7 Read Exception Status (FC: 07H). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 3.8 Diagnostics (FC: 08H) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

Return query data (sub-function code: 00H) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 Restart communications option (sub-function code: 01H). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 Return diagnostic register (sub-function code: 02H) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 Change ASCII input delimiter (sub-function code: 03H) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 Force listen only mode (sub-function code: 04H) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 Clear counters and diagnostic register (sub-function code: 0AH) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 Return bus message count (sub-function code: 0BH). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 Return bus communication error count (sub-function code: 0CH) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 Return bus exception error count (sub-function code: 0DH) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 Return slave message count (sub-function code: 0EH) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 Return slave no response count (sub-function code: 0FH) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32 Return slave NAK count (sub-function code: 10H) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33 Return slave busy count (sub-function code: 11H) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34 Return bus character overrun count (sub-function code: 12H) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35 Return IOP overrun error count (sub-function code: 13H). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36 Clear overrun counter and flag (sub-function code: 14H) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

3.9 Get Communications Event Counter (FC: 0BH) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38 3.10 Get Communications Event Log (FC: 0CH) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39 3.11 Write Multiple Coils (FC: 0FH) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41 3.12 Write Multiple Registers (FC: 10H). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42 3.13 Report Slave ID (FC: 11H) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 3.14 Read File Record (FC: 14H) (SC: 06H). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45 3.15 Write File Record (FC: 15H) (SC: 06H). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47

<![if ! IE]>

<![endif]>CONTENTS

3

3.16 Mask Write Register (FC: 16H) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48 3.17 Read/Write Multiple Registers (FC: 17H). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49

CHAPTER 4 EXCEPTION CODES	50
INDEX	52

REVISIONS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .54 WARRANTY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .55 TRADEMARKS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .56

4

RELEVANT MANUALS

Manual name [manual number]	Description	Available form
MELSEC iQ-R MODBUS and MODBUS/TCP	Protocol (MODBUS, MODBUS/TCP) that reads and writes data from a target	e-Manual
Reference Manual	device to a module	PDF
[BCN-P5999-1060] (this manual)

e-Manual refers to the Mitsubishi Electric FA electronic book manuals that can be browsed using a dedicated tool.

e-Manual has the following features:

•Required information can be cross-searched in multiple manuals.

•Other manuals can be accessed from the links in the manual.

•The hardware specifications of each part can be found from the product figures.

•Pages that users often browse can be bookmarked.

•Sample programs can be copied to an engineering tool.

TERMS

Unless otherwise specified, this manual uses the following terms.

Term	Description
Master	A name for the side that requests function execution
MODBUS device	A device used in communications via the MODBUS protocol
Request message	A message that requests function execution to slaves.
	In the MODBUS protocol, the master requests function execution to the slaves.
Response message	A message that returns execution results of functions from a slave to the master
Slave	A name for the side that processes execution requests from the master and returns the execution results

GENERIC TERMS AND ABBREVIATIONS

Unless otherwise specified, this manual uses the following generic terms and abbreviations.

Generic term/abbreviation	Description
C24	A MELSEC iQ-R series serial communication module
FC	An abbreviation of function code
SC	An abbreviation of sub code

5

Load the 16-bit register whose bits are all '1'.

1 FRAME SPECIFICATIONS

1.1 MODBUS Protocol Frame Specifications

This section describes the frame specifications of the MODBUS protocol.

	Address field			Function code			Data		Error check
					Protocol data unit
	Area name					Description
	Address field					■When request message is sent from the master to a slave
						• 0: Sends a request message to all the slaves. (Broadcast)
						• 1 to 247: Stores the target slave station number.
						■When response message is sent from a slave to the master
						The host station number is stored when sending a response message.
	Protocol data unit		Function code			■When request message is sent from the master to a slave
						Specifies the content of the processing instructed from the master to a slave.
						■When response message is sent from a slave to the master
						A requested function code is stored in the case of normal completion.
						The most significant bit turns ON in the case of error completion.
		Data				■When request message is sent from the master to a slave
						Stores the request content of the processing.
						■When response message is sent from a slave to the master
						Stores the execution result of the processing.
	Error check					The master adds a check code in a request message and transmits the request message.
						The slave, which received the request message, recalculates the check code in the request message
						and determines whether the message is correct or not.
						The message is discarded if it has an error.
						The error check method differs depending on the frame mode.

The following frame modes are available.

•RTU mode

•ASCII mode

The frame mode of C24 must be consistent with that of the target device.

RTU mode

In this mode, frames are received or sent in binary codes.

The frame specifications are compliant with the MODBUS protocol specifications.

	Start	Address field	Function code	Data	Error check	END	Address field
						(Start)
	3.5 character time	1 byte	1 byte	0 to 252 bytes	2 bytes	3.5 character time	1 byte
	or more					or more

Error check calculation range

Error check in RTU mode

The error check in the RTU mode is conducted by CRC (Cyclic Redundancy Check). C24 calculates the CRC by the following steps.

Follow the same steps to calculate the CRC when conducting an error check on the target device.

1.

2. The CRC is calculated every 8 bits from the upper bit of the frame.

Calculate the exclusive OR (XOR) from the 8 bits of the frame and the bits of the step 1.

3. Shift the result of step 2 by 1 bit to the right.

6	1 FRAME SPECIFICATIONS
	1.1 MODBUS Protocol Frame Specifications

	4.	If the least significant bit of the step 2 is '1', calculate the exclusive OR (XOR) from the result of step 3 and the generator
		polynomial (A001H).
			1
	If the least significant bit is '0', do not calculate the exclusive OR (XOR), but shift it by 1 bit to the right.
	5.	Repeat the step 3 and 4 until the bit is shifted up to 8 times.
	6.	Calculate the exclusive OR (XOR) from the result of step 5 and the next 8 bits of the frame.
	7.	Repeat the step 3 to 6.
	8.	Repeat the above operations until the end of the data unit is reached. The final value is a calculated CRC value.
	9.	The CRC value is stored in the frame in the order of lower 8 bits to upper 8 bits.

Ex.

The following is a calculation example in the case where function code 07H is sent to station No.2.

Error check range is as follows:

•Address field (1 byte): 02H

•Function code (1 byte): 07H

•Data (0 bytes)

CRC error checking procedure		16-bit register (MSB)			Flag*1
1	Load the 16-bit register whose bits are all '1'.	16-bit register whose bits are all '1'.	1111 1111	1111 1111
2	Calculate the exclusive OR (XOR) from the first 8 bits of the	Address field (02H)		0000 0010
	frame and the bits in the above.
		Exclusive OR (XOR)	1111 1111	1111 1101
3	Shift by 1 bit to the right.	Shift 1	0111 1111	1111 1110	1
4	Since the flag is '1', calculate the exclusive OR (XOR) from the	Generator polynomial (A001H)	1010 0000	0000 0001
	result in 'Shift 1' and generator polynomial (A001H).
		Exclusive OR (XOR)	1101 1111	1111 1111
5	Shift by 1 bit to the right.	Shift 2	0110 1111	1111 1111	1
	Since the flag is '1', calculate the exclusive OR (XOR) from the	Generator polynomial (A001H)	1010 0000	0000 0001
	result in 'Shift 2' and generator polynomial (A001H).
		Exclusive OR (XOR)	1100 1111	1111 1110
	Shift by 1 bit to the right.	Shift 3	0110 0111	1111 1111	0
	Shift by 1 bit to the right.	Shift 4	0011 0011	1111 1111	1
	Since the flag is '1', calculate the exclusive OR (XOR) from the	Generator polynomial (A001H)	1010 0000	0000 0001
	result in 'Shift 4' and generator polynomial (A001H).
		Exclusive OR (XOR)	1001 0011	1111 1110
	Shift by 1 bit to the right.	Shift 5	0100 1001	1111 1111	0
	Shift by 1 bit to the right.	Shift 6	0010 0100	1111 1111	1
	Since the flag is '1', calculate the exclusive OR (XOR) from the	Generator polynomial (A001H)	1010 0000	0000 0001
	result in 'Shift 6' and generator polynomial (A001H).
		Exclusive OR (XOR)	1000 0100	1111 1110
	Shift by 1 bit to the right.	Shift 7	0100 0010	0111 1111	0
	Shift by 1 bit to the right.	Shift 8	0010 0001	0011 1111	1
	Since the flag is '1', calculate the exclusive OR (XOR) from the	Generator polynomial (A001H)	1010 0000	0000 0001
	result in 'Shift 8' and generator polynomial (A001H).
		Exclusive OR (XOR)	1000 0001	0011 1110
6	Calculate the exclusive OR (XOR) from the next 8 bits of the	Function code (07H)		0000 0111
	frame and the bits in the above.
		Exclusive OR (XOR)	1000 0001	0011 1001

1 FRAME SPECIFICATIONS	7
1.1 MODBUS Protocol Frame Specifications

CRC error checking procedure		16-bit register (MSB)			Flag*1
7	Shift by 1 bit to the right.	Shift 1	0100 0000	1001 1100	1
	Since the flag is '1', calculate the exclusive OR (XOR) from the	Generator polynomial (A001H)	1010 0000	0000 0001
	result in 'Shift 1' and generator polynomial (A001H).
		Exclusive OR (XOR)	1110 0000	1001 1101
	Shift by 1 bit to the right.	Shift 2	0111 0000	0100 1110	1
	Since the flag is '1', calculate the exclusive OR (XOR) from the	Generator polynomial (A001H)	1010 0000	0000 0001
	result in 'Shift 2' and generator polynomial (A001H).
		Exclusive OR (XOR)	1101 0000	0100 1111
	Shift by 1 bit to the right.	Shift 3	0110 1000	0010 0111	1
	Since the flag is '1', calculate the exclusive OR (XOR) from the	Generator polynomial (A001H)	1010 0000	0000 0001
	result in 'Shift 3' and generator polynomial (A001H).
		Exclusive OR (XOR)	1100 1000	0010 1110
	Shift by 1 bit to the right.	Shift 4	0110 0100	0001 0011	0
	Shift by 1 bit to the right.	Shift 5	0011 0010	0000 1001	1
	Since the flag is '1', calculate the exclusive OR (XOR) from the	Generator polynomial (A001H)	1010 0000	0000 0001
	result in 'Shift 5' and generator polynomial (A001H).
		Exclusive OR (XOR)	1001 0010	0000 1000
	Shift by 1 bit to the right.	Shift 6	0100 1001	0000 0100	0
	Shift by 1 bit to the right.	Shift 7	0010 0100	1000 0010	0
	Shift by 1 bit to the right.	Shift 8	0001 0010	0100 0001	0
8	The final value is a calculated CRC value.	CRC value	12H	41H

*1 The least significant bit from the previous exclusive OR (XOR)

Data is stored as follows:

Address field	Function code	Error check
		Lower 8 bits of the CRC value	Upper 8 bits of the CRC value
02H	07H	41H	12H

ASCII mode

In this mode, frames are received or sent in units of 2 characters (2 bytes) in ASCII codes.

The frame specifications are compliant with the MODBUS protocol specifications.

Start	Address field	Function code			Data	Error check		END
:	2 characters	2 characters			n x 2 characters	2 characters		CR + LF
(3AH)					(n = 0 to 252)			(0DH) (0AH)
		Error check calculation range

Error check in ASCII mode

The error check in the ASCII mode is conducted by LRC (Longitudinal Redundancy Check). C24 calculates the LRC by the following steps.

Follow the same steps to calculate the LRC when conducting an error check on the target device.

1.

2.

3.

4.

To calculate the LRC, convert the ASCII codes within the error check range into the RTU format (binary).

Add the figures in units of contiguous 8 bits in the frame. (Excluding carries during addition.)

Change the result of step 2 to a 2's complement. (Reverse the bits and add 01H.)

Convert the result of step 3 to an ASCII code.

Ex.

The following are calculation examples in the case where function code 01H is sent to station No.2. Error check range of the request message is as follows:

•Address field (1 byte): 02H

•Function code (1 byte): 01H

8	1 FRAME SPECIFICATIONS
	1.1 MODBUS Protocol Frame Specifications

• Data (2 bytes): Start coil number specification (0000H), Number of read points (0008H)

Error check procedure		LRC in request message transmission
							1
1	Convert the ASCII codes within the error check range into the RTU format	Address field (02H)		0000	0010
	(binary).
		Function code (01H)		0000	0001
		Start coil number specification (H)		0000	0000
		Start coil number specification (L)		0000	0000
		Read points (H)		0000	0000
		Read points (L)		0000	1000
2	Add the figures. (Excluding carries during addition.)	Addition result		0000	1011
3	Change the result to a 2's complement. (Reverse the bits and add 01H.)	Reversed bit value		1111	0100
		01H		0000	0001
		LRC value		1111	0101
4	Convert the result to an ASCII code.	LRC value (ASCII code)		F	5
				46H	35H

Data is stored in ASCII code as follows:

Data	Address field		Function code		Start coil number				Read points				Error check
category					specification
Value	02H		01H		0000H				0008H				F5H
Character	0	2	0	1	0	0	0	0	0	0	0	8	F	5
RTU (binary)	0000	0010	0000	0001	0000	0000	0000	0000	0000	0000	0000	1000	1111	0101
ASCII code	30H	32H	30H	31H	30H	30H	30H	30H	30H	30H	30H	38H	46H	35H

The slave, which received the request message, recalculates the check code in the request message and determines whether the message is correct or not.

Error check procedure		LRC check when receiving a request message
1	Convert the ASCII codes within the error check range into the RTU format	Address field (02H)	0000	0010
	(binary).
		Function code (01H)	0000	0001
		Start coil number specification (H)	0000	0000
		Start coil number specification (L)	0000	0000
		Read points (H)	0000	0000
		Read points (L)	0000	1000
2	Add the LRC value. (Excluding carries during addition.)	LRC value	1111	0101
	Normally, the addition result is zero.
		Addition result	0000	0000

1 FRAME SPECIFICATIONS	9
1.1 MODBUS Protocol Frame Specifications

1.2 MODBUS/TCP Protocol Frame Specifications

This section describes the frame specifications of the MODBUS/TCP protocol.

MODBUS/TCP frame	Ethernet	IP header	TCP header			Application data				FCS
	header									(Error check)
						MODBUS/TCP application data unit
	MODBUS application header						Protocol data unit
	Transaction	Protocol ID	Message			Module ID	Function code	Data
	ID		length

Area name		Area size	Description
MODBUS application header	Communication ID	2 bytes	Used by the master to match response messages from slaves.
	Protocol ID	2 bytes	Indicates the protocol of the protocol data unit.
			For MODBUS/TCP, 0 is stored.
	Message length	2 bytes	Stores the message size in bytes.
			The stored message length indicates the length of the message in
			areas subsequent to this area.
	Module ID	1 byte	Used when specifying slaves connected to other lines, such as with
			the MODBUS Serial protocol.
Protocol data unit	Function code	1 byte	Specifies the content of the processing instructed from the master to a
			slave.
	Data	1 to 252 bytes	■When request message is sent from the master to a slave
			Stores the request content of the processing.
			■When response message is sent from a slave to the master
			Stores the execution result of the processing.

10	1 FRAME SPECIFICATIONS
	1.2 MODBUS/TCP Protocol Frame Specifications

1.3 Protocol Data Unit Formats Grouped by Function

1

This section describes the protocol data unit formats of the MODBUS standard functions.

When the device number is specified within the message

When specifying the device number within the message, specify "device number - 1".

However, this instruction is not applicable to the file number and the device number specified for reading or writing extended file register.

Ex.

When the status of input 32 (100032) is read by the read discrete inputs (function code: 02H)

Function code		Data
	Start input number specification			Number of read points
02H		(1)			0001H
		001FH
	(H)	(L)		(H)	(L)

(1) When reading the status of input 32 (100032), specify 31 (001FH) for the start input number.

The device number stored in the response message is "the device number of the device that actually performed reading/ writing - 1".

Descriptions of request message and response message formats

This section describes descriptions of the request message and response message formats of the MODBUS standard functions.

■ Message format for MODBUS RTU mode and MODBUS/TCP

(1)	Function code		Data
(2)		Start coil number specification		Number of read points
(3)	01H	(0000H to FFFFH)		(0001H to 07D0H)
		(H)	(L)	(H)	(L)

	1 byte	1 byte	(4)
	(8 bits)	(8 bits)

(1)Area name

(2)Frame description

(3)For request message format: Setting range

For response message format: Value stored in the response message

(4)When one piece of data consists of two bytes, the upper byte (eight bits) is (H) and the lower byte (eight bits) is (L).

■Message format for MODBUS ASCII mode

The message format shown in Chapter 3 is for RTU mode or MODBUS/TCP.

In the ASCII mode, read the values shown in Chapter 3 in ASCII code.

1 FRAME SPECIFICATIONS	11
1.3 Protocol Data Unit Formats Grouped by Function

(RTU mode)	Function code		Data
		Start coil number specification			Number of read points
	01H		(006EH)			(003FH)
		(H)	(L)		(H)	(L)

Convert RTU mode to ASCII mode

(ASCII mode)

Function code						Data
			Start coil number specification					Number of read points
0	1	0	0	6	E		0	0	3	F
(30H)	(31H)	(30H)	(30H)	(36H)	(45H)		(30H)	(30H)	(33H)	(46H)
(H)	(L)	(H)			(L)		(H)			(L)

■ Response message format

The format of the response message sent from a slave to the master varies depending on whether the processing performed by the slave completed successfully or completed with an error.

In the MODBUS standard function, the formats when completed successfully and completed with an error are described in the response message format.

Storage locations of exception code and error code

When processing on a slave is completed with an error, an exception code is sent to the master. For details on exception codes, refer to the following.

Page 50 EXCEPTION CODES

Exception codes are also stored in the buffer memory of modules. The detailed cause is detected as an error by modules.

For details on the buffer memory and errors of modules, refer to the following.MELSEC iQ-R Ethernet User's Manual (Application)

MELSEC iQ-R Serial Communication Module User's Manual(Application)

12	1 FRAME SPECIFICATIONS
	1.3 Protocol Data Unit Formats Grouped by Function

2	MODBUS STANDARD FUNCTION LIST
This chapter lists the MODBUS standard functions and availability for modules when using the slave function.
The modules are abbreviated as follows:
								2
• C24: RJ71C24, RJ71C24-R2, RJ71C24-R4
• E71: RJ71EN71, R04ENCPU, R08ENCPU, R16ENCPU, R32ENCPU, R120ENCPU
: Available, : Not available
Function code		Sub code (SC)	Function name	C24	E71	Reference
(FC)
01H			Read coils			Page 14 Read Coils (FC: 01H)
02H			Read discrete inputs			Page 15 Read Discrete Inputs (FC: 02H)
03H			Read holding registers			Page 16 Read Holding Registers (FC: 03H)
04H			Read input registers			Page 17 Read Input Registers (FC: 04H)
05H			Write single coil			Page 18 Write Single Coil (FC: 05H)
06H			Write single register			Page 19 Write Single Register (FC: 06H)
07H			Read exception status			Page 20 Read Exception Status (FC: 07H)
08H			Page 13 Diagnosis function			Page 21 Diagnostics (FC: 08H)
			details
0BH			Get communications event			Page 38 Get Communications Event Counter (FC: 0BH)
			counter
0CH			Get communications event log			Page 39 Get Communications Event Log (FC: 0CH)
0FH			Write multiple coils			Page 41 Write Multiple Coils (FC: 0FH)
10H			Write multiple registers			Page 42 Write Multiple Registers (FC: 10H)
11H			Report slave ID			Page 43 Report Slave ID (FC: 11H)
14H		06H	Read file record			Page 45 Read File Record (FC: 14H) (SC: 06H)
15H		06H	Write file record			Page 47 Write File Record (FC: 15H) (SC: 06H)
16H			Mask write register			Page 48 Mask Write Register (FC: 16H)
17H			Read/Write multiple registers			Page 49 Read/Write Multiple Registers (FC: 17H)
Diagnosis function details
Function code		Sub-function	Function name	Reference
(FC)		code
08H		0000H	Return query data	Page 22 Return query data (sub-function code: 00H)
		0001H	Restart communications option	Page 23 Restart communications option (sub-function code: 01H)
		0002H	Return diagnostic register	Page 24 Return diagnostic register (sub-function code: 02H)
		0003H	Change ASCII input delimiter	Page 25 Change ASCII input delimiter (sub-function code: 03H)
		0004H	Force listen only mode	Page 26 Force listen only mode (sub-function code: 04H)
		000AH	Clear counters and diagnostic	Page 27 Clear counters and diagnostic register (sub-function code: 0AH)
			register
		000BH	Return bus message count	Page 28 Return bus message count (sub-function code: 0BH)
		000CH	Return bus communication error	Page 29 Return bus communication error count (sub-function code: 0CH)
			count
		000DH	Return bus exception error count	Page 30 Return bus exception error count (sub-function code: 0DH)
		000EH	Return slave message count	Page 31 Return slave message count (sub-function code: 0EH)
		000FH	Return slave no response count	Page 32 Return slave no response count (sub-function code: 0FH)
		0010H	Return slave NAK count	Page 33 Return slave NAK count (sub-function code: 10H)
		0011H	Return slave busy count	Page 34 Return slave busy count (sub-function code: 11H)
		0012H	Return bus character overrun	Page 35 Return bus character overrun count (sub-function code: 12H)
			count
		0013H	Return IOP overrun error count	Page 36 Return IOP overrun error count (sub-function code: 13H)
		0014H	Clear overrun counter and flag	Page 37 Clear overrun counter and flag (sub-function code: 14H)

2 MODBUS STANDARD FUNCTION LIST	13

3 MODBUS STANDARD FUNCTION DETAILS

This chapter describes protocol data unit formats.

3.1 Read Coils (FC: 01H)

Operation description

Reads the status (ON/OFF) of one or multiple coils.

Request message format (from master to slave)

Function code		Data
	Start coil number specification			Number of read points
01H	(0000H to FFFFH)			(0001H to 07D0H)
	(H)	(L)		(H)	(L)

Response message format (from slave to master)

■ When completed successfully

Function code					Data
	Number of read				Device data 1			Device data n
	bytes n
01H
					Number of read bytes n

• Device data 1 to n

b7	b6	b5	b4	b3	b2	b1	b0
Device data 1							Bit device storage order

Device data n		0: OFF
		1: ON

•The read coil status is stored in the order of lower bit to higher bit.

•If the number of read points is not a multiple of eight, the remaining bits are all set to 0.

■ When completed with an error

Function code

Data

Exception code

81H

14	3 MODBUS STANDARD FUNCTION DETAILS
	3.1 Read Coils (FC: 01H)

3.2 Read Discrete Inputs (FC: 02H)

Operation description

Reads the status (ON/OFF) of one or multiple inputs.

Request message format (from master to slave)

Function code		Data			3
	Start input number specification			Number of read points
02H	(0000H to FFFFH)			(0001H to 07D0H)
	(H)	(L)		(H)	(L)

Response message format (from slave to master)

■ When completed successfully

Function code					Data
	Number of read				Device data 1			Device data n
	bytes n
02H
					Number of read bytes n

• Device data 1 to n

b7	b6	b5	b4	b3	b2	b1	b0
Device data 1							Bit device storage order

Device data n		0: OFF
		1: ON

•The read input status is stored in the order of lower bit to higher bit.

•If the number of read points is not a multiple of eight, the remaining bits are all set to 0.

■ When completed with an error

Function code

Data

Exception code

82H

3 MODBUS STANDARD FUNCTION DETAILS	15
3.2 Read Discrete Inputs (FC: 02H)

3.3 Read Holding Registers (FC: 03H)

Operation description

Reads one or multiple holding register values.

Request message format (from master to slave)

Function code			Data
	Start holding register number			Number of read points
	specification
03H	(0000H to FFFFH)			(0001H to 007DH)
	(H)	(L)		(H)	(L)

Response message format (from slave to master)

■ When completed successfully

Function code					Data
	Number of read		Device data 1				Device data n
	bytes n×2
03H			(H)	(L)			(H)	(L)

Number of read bytes n×2

• For example, when n = 4, the number of read bytes is 4 2 = 8.

■ When completed with an error

Function code

Data

Exception code

83H

16	3 MODBUS STANDARD FUNCTION DETAILS
	3.3 Read Holding Registers (FC: 03H)