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Modbus-RTU Slave System
Section 9-1
9-1
Modbus-RTU Slave System
A Modbus-RTU Slave System can be used to send Modbus-RTU commands
from a host computer (e.g., personal computer) to a PLC to read and write I/O
memory.
Host-initiated
Communications
Communications in a Modbus-RTU Slave System are started by the host
computer.
The host computer sends a command to the PLC. The PLC processes the
command and returns a response to the host computer. This process is
repeated, allowing the host computer to monitor and control PLC operation.
Note
Only Modbus-RTU slave mode is supported. A Modbus-ASCII slave mode is
not supported by the Serial Communications Boards or Serial Communica-
tions Units.
Modbus-RTU Specifications
Note
1.
Modbus-ASCII mode is not supported.
2.
The data length is fixed at 8 bits and cannot be changed by the user.
3.
The number of stop bits is automatically determined by the parity and can-
not be set by the user.
4.
The address cannot be set to 0. In commands, 0 is used to indicate broad-
cast commands.
9-1-1
Communicating with CS/CJ-series CPU Units Using Modbus
There are four data models that are defined for Modbus. Settings in the DM
Area are used to the I/O memory area in the CS/CJ-series CPU Unit corre-
sponding to each of these data models for use by the Serial Communications
Board/Unit. The I/O memory areas that can be set for each of the Modbus
data models are given below.
1.
Discrete inputs:
CIO Area (fixed)
2.
Coils:
CIO, Work, Holding, or Auxiliary Area
3.
Input Registers:
CIO, Work, Holding, or Auxiliary Area
4.
Holding Registers: DM or EM Area
Host computer
CS/CJ-series PLC
Command
Response
Item
Description
Mode
Modbus-RTU slave mode (See note 1.)
Baud rate
1,200/2,400/4,800/9,600/19,200/38,400/57,600/115,200 bps
Default: 19,200 bps
Data length
8 bits (See note 2.)
Parity
Odd, even, or none
Default: Even
Stop bits
Odd or even parity:1 bit
No parity: 2 bits (See note 3.)
Address setting
range
1 to 247 (broadcasting: 0) (See note 4.)
Frame format
Slave address: 1 byte
Function code: 1 byte
Data: 0 to 252 bytes
CRC code: 2 bytes
Содержание SYSMAC CJ1W-SCU21-V1
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Страница 89: ...60 Basic Operating Procedure Section 1 9...
Страница 151: ...122 RS 232C and RS 422A 485 Wiring Section 3 4...
Страница 173: ...144 Host Link Function for Replacing Existing PLCs Section 4 6...
Страница 223: ...194 Enhanced Protocol Macro Functions Section 5 6...
Страница 277: ...248 Communications Frames Section 6 8...
Страница 291: ...262 Basic Operating Procedure in No protocol Mode Section 7 4...
Страница 301: ...272 Auxiliary Area and CIO Area Allocations Section 8 3...
Страница 391: ...362 Introduction Appendix A...
Страница 421: ...392 CompoWay F Master Protocol Appendix B...
Страница 513: ...484 E5 K Digital Controller Read Protocol Appendix F...
Страница 571: ...542 E5ZE Temperature Controller Write Protocol Appendix I...
Страница 587: ...558 E5 J Temperature Controller Protocol Appendix J...
Страница 627: ...598 ES100 Digital Controller Protocol Appendix K...
Страница 661: ...632 V500 V520 Bar Code Reader Protocol Appendix M...
Страница 697: ...668 3Z4L Laser Micrometer Protocol Appendix N...
Страница 717: ...688 Visual Inspection System Protocol Appendix O...
Страница 755: ...726 V600 V620 ID Controller Protocol Appendix P...
Страница 763: ...734 Hayes Modem AT Command Protocol Appendix Q...
Страница 767: ...738 Changing Communications Port Settings Using STUP 237 Appendix R...
Страница 781: ...752 Revision History...