Modes, RTU mode, Ascii mode, Lrc | Schneider Electric VW3 A3 303

8. Modbus protocol

8. 2. Modes

bRTU mode

The Modbus RTU frame contains no message header byte, nor end of message bytes. It is defined as follows:

Slave address

Function code

Data

CRC16

The data is transmitted in binary code. CRC16: Cyclic redundancy check parameter.

The end of the frame is detected on a silence greater than or equal to 3.5 characters. The format used for the frames in the rest of this document is RTU mode.

bASCII mode

The structure of the Modbus ASCII frame is as follows:

Header	Slave	Function		Data
":"	address	code

LRC

HiLo

End

"CR" "LF"

Header: By default, ":" = 16#3A. Two other characters are possible: "CR" = 16#0D and "LF" = 16#0A.

LRC: The 2's-complement of the modulo 256 sum (in hexadecimal format) of the frame (excluding the header and end characters) before ASCII coding.

Example: Write a value of 10 to logic address word 9001 (16#2329) on slave 2

Identical request and response:

In hexadecimal format

3A

30 32

30 36

32 33 32 39

30 30 30 41

41 32

0D

0A

In ASCII format

:

0

2

0 6

2

3

2

9

0 0 0 A

A 2

CR

LF

26

Image 26

Schneider Electric VW3 A3 303 user manual Modes, RTU mode, Ascii mode, Slave address Function code Data, Lrc

Contents

Altivar Contents Before you begin Electric shock will result in death or serious injury Programming Manual Installation ManualDocumentation structure Communication Parameters Manual Notation IntroductionPresentation Receipt Hardware setupInstalling the card in the drive Hardware description Coding the address Switch codingChoosing polarization Address 1234 Modbus RS485 standard Connecting to the busWiring recommendations Connection cables Connection via RJ45 wiring systemConnection accessories TWD XCA RJ030 Connection cables for the masterType of master Master interface Description Catalog number TSX SCP CM RS485 double shielded twisted pair Connection via junction boxesDescription Catalog Number Subscriber socket Cables TSX CSA500 TSX P ACC Configuration Communication parameters Control via Modbus or the terminals in I/O profile Control CommandControl via Modbus in I/O profile Parameter Value Comment Control via Modbus in Drivecom profile Control via Modbus or the terminals in Drivecom profile Configuration RDY NET Example of configuration via the graphic display terminalCommunication scanner COM. Scanner Input Communication faults COM. Fault Management Format CONFIG. COMM. MAPMonitored parameters Format Range Terminal display LEDs DiagnosticsChecking the address Green RUN Red ERR Meaning Corrective action COM. Scanner Input MAP RUN NETCommunication MAP COM Scan Output MAP CMD. Word Image COM Scan Output MAP Input variable Scanner parameterOutput variable Scanner parameter Communication fault Card fault Slave Slave j Slave k Modbus protocolPrinciple Modes RTU modeAscii mode Slave address Function code Data Code Modbus name Description Broadcast Size of data Modbus functions availableRead Holding/Input Registers 3/4 Write Single Register Diagnostics Get Comm Event Counter 11 = 16#0B Write Multiple Registers 16 = 16#10 Read/Write Multiple Registers 23 = 16#17 Read Device Identification 43 = 16#2B Machine Example of positive response MEI Code Modbus name Description Size of data Output variables Logic address Default assignmentInput variables Logic address Default assignment Parameter Logic Input variable address Logic address Default valueParameter Logic Read Input monitoring Output controlParameter assigned Value Parameter assigned Response Code Error codeException responses Read non-existent or protected parameters Logic address Parameter Value Appendix RS485 standard Modbus 2-wire standard schematic Master Modbus 4-wire standard schematic Uni-Telway schematic Wire Jbus schematic Type of trunk cable Cable with 1 shielded twisted pair Recommendations Creating a Modbus bus using non-standard equipmentDifferent scenarios Calculating the polarization Example Contact no. Signal RS485 schematic for the cardCard connector pinout SUB-D Atv71ModbusJbusENV1 2005-05