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
(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.
(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
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
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
Reference Manual
[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.
Protocol (MODBUS, MODBUS/TCP) that reads and writes data from a target
device to a module
e-Manual
PDF
TERMS
Unless otherwise specified, this manual uses the following terms.
Ter m 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.
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
In the MODBUS protocol, the master requests function execution to the slaves.
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
1 FRAME SPECIFICATIONS
DataAddress field Function code Error check
Protocol data unit
Start
END
(Start)
DataAddress field Function code Error check Address field
3.5 character time
or more
1 byte 1 byte
0 to 252 bytes
2 bytes
3.5 character time
or more
1 byte
Error check calculation range
1.1 MODBUS Protocol Frame Specifications
This section describes the frame specifications of the MODBUS protocol.
Area name Description
Address field ■When request message is sent from the master to a slave
Protocol data unit Function code ■When request message is sent from the master to a slave
Data ■When request message is sent from the master to a slave
Error check The master adds a check code in a request message and transmits the request message.
The following frame modes are available.
• RTU mode
• ASCII mode
The frame mode of C24 must be consistent with that of the target device.
• 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.
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.
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.
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.
6
RTU mode
In this mode, frames are received or sent in binary codes.
The frame specifications are compliant with the MODBUS protocol specifications.
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. Load the 16-bit register whose bits are all '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.
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
Ex.
polynomial (A001H).
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.
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 Loa d the 1 6 -b i t reg i ste r w hos e b its a re al l '1' . 16 - bit r egis t er w h o se b i ts a r e all ' 1'. 1111 1111 1111 1111
2 Calculate the exclusive OR (XOR) from the first 8 bits of the
frame and the bits in the above.
3 S h ift b y 1 bi t t o th e rig h t . Sh i ft 1 0111 1111 1111 111 0 1
4 Since the flag is '1', calculate the exclusive OR (XOR) from the
result in 'Shift 1' and generator polynomial (A001H).
5 S h ift b y 1 bi t t o th e rig h t . Sh i ft 2 011 0 1111 1111 1111 1
Since the flag is '1', calculate the exclusive OR (XOR) from the
result in 'Shift 2' and generator polynomial (A001H).
Sh i ft b y 1 bit t o the r igh t . Sh i f t 3 0110 0 111 1111 1111 0
Sh i ft b y 1 bit t o the r igh t . Sh i f t 4 0011 0 011 1111 1111 1
Since the flag is '1', calculate the exclusive OR (XOR) from the
result in 'Shift 4' and generator polynomial (A001H).
Sh i ft b y 1 bit t o the r igh t . Sh i f t 5 010 0 100 1 1111 1111 0
Sh i ft b y 1 bit t o the r igh t . Sh i f t 6 001 0 010 0 1111 1111 1
Since the flag is '1', calculate the exclusive OR (XOR) from the
result in 'Shift 6' and generator polynomial (A001H).
Sh i ft b y 1 bit t o the r igh t . Sh i f t 7 010 0 001 0 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
result in 'Shift 8' and generator polynomial (A001H).
6 Calculate the exclusive OR (XOR) from the next 8 bits of the
frame and the bits in the above.
Address field (02H) 0000 0010
Ex c lus i ve OR ( XOR ) 1111 1111 1111 11 0 1
Generator polynomial (A001H) 1010 0000 0000 0001
Ex c lus i ve OR ( XOR ) 110 1 1111 1111 1111
Generator polynomial (A001H) 1010 0000 0000 0001
Ex c lus i ve OR ( XOR ) 110 0 1111 1111 111 0
Generator polynomial (A001H) 1010 0000 0000 0001
Ex c lus i ve OR ( XOR ) 10 0 1 00 11 1111 111 0
Generator polynomial (A001H) 1010 0000 0000 0001
Ex c lus i ve OR ( XOR ) 10 0 0 01 0 0 1111 111 0
Generator polynomial (A001H) 1010 0000 0000 0001
Exclusive OR (XOR) 1000 0001 0011 1110
Function code (07H) 0000 0111
Exclusive OR (XOR) 1000 0001 0011 1001
*1
1
1 FRAME SPECIFICATIONS
1.1 MODBUS Protocol Frame Specifications
7
Ex.
CRC error checking procedure 16-bit register (MSB) Flag
Start END
:
(3AH)
CR + LF
(0DH) (0AH)
Address field
2 characters
Function code
2 characters
Data Error check
n x 2 characters
(n = 0 to 252)
2 characters
Error check calculation range
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
result in 'Shift 1' and generator polynomial (A001H).
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
result in 'Shift 2' and generator polynomial (A001H).
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
result in 'Shift 3' and generator polynomial (A001H).
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
result in 'Shift 5' and generator polynomial (A001H).
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)
Generator polynomial (A001H) 1010 0000 0000 0001
Exclusive OR (XOR) 1110 0000 1001 1101
Generator polynomial (A001H) 1010 0000 0000 0001
Ex c lus i ve OR ( XOR ) 110 1 000 0 01 0 0 1111
Generator polynomial (A001H) 1010 0000 0000 0001
Exclusive OR (XOR) 1100 1000 0010 1110
Generator polynomial (A001H) 1010 0000 0000 0001
Exclusive OR (XOR) 1001 0010 0000 1000
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
*1
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.
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. To calculate the LRC, convert the ASCII codes within the error check range into the RTU format (binary).
2. Add the figures in units of contiguous 8 bits in the frame. (Excluding carries during addition.)
3. Change the result of step 2 to a 2's complement. (Reverse the bits and add 01H.)
4. Convert the result of step 3 to an ASCII code.
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 Convert the ASCII codes within the error check range into the RTU format
(binary).
2 Add the figures. (Excluding carries during addition.) Addition result 0000 1011
3 C h ang e the r e sul t t o a 2 ' s com p leme n t. ( R eve r s e th e b its a n d ad d 01H . ) Rev e r sed b it va l ue 1111 010 0
4 Convert the result to an ASCII code. LRC value (ASCII code) F 5
Address field (02H) 0000 0010
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
01H 0000 0001
LR C val u e 1111 010 1
46H 35H
Data is stored in ASCII code as follows:
Data
category
Value 02H 01H 0000H 0008H F5H
Character0 2 0 1 00000008F5
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
Address field Function code Start coil number
specification
Read points Error check
1
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
(binary).
2 Add the LRC value. (Excluding carries during addition.)
Normally, the addition result is zero.
Address field (02H) 0000 0010
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
LR C val u e 1111 010 1
Addition result 0000 0000
1 FRAME SPECIFICATIONS
1.1 MODBUS Protocol Frame Specifications
9
1.2 MODBUS/TCP Protocol Frame Specifications
FCSEthernet
header
Application dataIP header TCP header
(Error check)
MODBUS/TCP frame
MODBUS/TCP application data unit
MODBUS application header
Transaction IDProtocol ID Message
length
Module ID Function code Data
Protocol data unit
This section describes the frame specifications of the MODBUS/TCP protocol.
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.
Module ID 1 byte Used when specifying slaves connected to other lines, such as with
Protocol data unit Function code 1 byte Specifies the content of the processing instructed from the master to a
Data 1 to 252 bytes ■When request message is sent from the master to a slave
The stored message length indicates the length of the message in
areas subsequent to this area.
the MODBUS Serial protocol.
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
Ex.
(H) (L)
(1)
(H) (L)
02H 001FH 0001H
Start input number specification
Data
Number of read points
Function code
(H) (L) (H) (L)
01H
(1)
(2)
(3)
(4)
Start coil number specification
Data
Number of read points
Function code
1 byte
(8 bits)
1 byte
(8 bits)
(0000H to FFFFH) (0001H to 07D0H)
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.
When the status of input 32 (100032) is read by the read discrete inputs (function code: 02H)
(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.
1
■ Message format for MODBUS RTU mode and MODBUS/TCP
(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
1.3 Protocol Data Unit Formats Grouped by Function
11
■ Response message format
(H) (L) (H) (L)
01H
(H) (L) (H) (L) (H)
(L)
(30H) (31H) (30H) (30H) (36H) (45H) (30H) (30H) (33H) (46H)
0 FE61 30000
(006EH) (003FH)
Start coil number specification
Data
Number of read points
Function code
Data
Start coil number specification
Number of read points
Function code
(RTU mode)
(ASCII mode)
Convert RTU mode to ASCII mode
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:
• C24: RJ71C24, RJ71C24-R2, RJ71C24-R4
• E71: RJ71EN71, R04ENCPU, R08ENCPU, R16ENCPU, R32ENCPU, R120ENCPU
: Available, : Not available
Function code
(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
0BH Get communications event
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)
Sub code (SC) Function name C24 E71 Reference
Page 21 Diagnostics (FC: 08H)
details
Page 38 Get Communications Event Counter (FC: 0BH)
counter
2
Diagnosis function details
Function code
(FC)
08H 0000H Return query data Page 22 Return query data (sub-function code: 00H)
Sub-function
code
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
000BH Return bus message count Page 28 Return bus message count (sub-function code: 0BH)
000CH Return bus communication error
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
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)
Function name Reference
Page 27 Clear counters and diagnostic register (sub-function code: 0AH)
register
Page 29 Return bus communication error count (sub-function code: 0CH)
count
Page 35 Return bus character overrun count (sub-function code: 12H)
count
2 MODBUS STANDARD FUNCTION LIST
13
3 MODBUS STANDARD FUNCTION DETAILS
(H) (L) (H) (L)
01H
Data
Number of read pointsStart coil number specification
Function code
(0000H to FFFFH) (0001H to 07D0H)
01H
DataFunction code
Number of read
bytes n
Device data 1 Device data n
Number of read bytes n
b0b1b2b3b4b5b6b7
0: OFF
1: ON
Device data 1
Device data n
Bit device storage order
81H
Data
Exception code
Function code
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)
Response message format (from slave to master)
■ When completed successfully
14
• Device data 1 to n
• 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
3 MODBUS STANDARD FUNCTION DETAILS
3.1 Read Coils (FC: 01H)
3.2 Read Discrete Inputs (FC: 02H)
(H) (L) (H) (L)
02H
Start input number specification
Data
Number of read points
Function code
(0000H to FFFFH) (0001H to 07D0H)
02H
DataFunction code
Number of read
bytes n
Device data 1 Device data n
Number of read bytes n
b0b1b2b3b4b5b6b7
0: OFF
1: ON
Device data 1
Device data n
Bit device storage order
82H
Data
Exception code
Function code
Operation description
Reads the status (ON/OFF) of one or multiple inputs.
Request message format (from master to slave)
Response message format (from slave to master)
■ When completed successfully
3
• Device data 1 to n
• 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
3 MODBUS STANDARD FUNCTION DETAILS
3.2 Read Discrete Inputs (FC: 02H)
15
3.3 Read Holding Registers (FC: 03H)
(H) (L) (H) (L)
03H
Start holding register number
specification
Data
Number of read points
Function code
(0000H to FFFFH) (0001H to 007DH)
03H
(H) (L) (H) (L)
DataFunction code
Number of read
bytes n×2
Device data 1 Device data n
Number of read bytes n×2
83H
Data
Exception code
Function code
Operation description
Reads one or multiple holding register values.
Request message format (from master to slave)
Response message format (from slave to master)
■ When completed successfully
• For example, when n = 4, the number of read bytes is 4 2 = 8.
■ When completed with an error
16
3 MODBUS STANDARD FUNCTION DETAILS
3.3 Read Holding Registers (FC: 03H)
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