Modbus Communication

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Modbus Communication

SUMMARY

This document describes the functionality and settings for Modbus-Master and Modbus-Slave.

Master-Functionality
Slave-Functionality
Status-Analysis
SoftPLC7.ini

Master-Functionality

Introduction

Via library functions the SoftPLC7 as a Modbus-Master can, using the serial interface, collect data from one or more Modbus-Slaves and allocate them for the application program.

The modules work similar to AG_SEND/AG_RECV found in the “alpha-bit Library”.
The SoftPLC7 supports the following Modbus-Functioncodes:

Functioncode	Name	HLL-Function within SoftPLC7 Modbus.dll	FC-Number
1	Read Coil Status	Modbus Read Coil Status	2001
2	Read Input Status	Modbus Read Input Status	2002
3	Read Holding Register	Modbus Read Holding Register	2003
4	Read Input Register	Modbus Read Input Register	2004
5	Force Single Coil	Modbus Force Single Coil	2005
6	Preset Single Register	Modbus Preset Single Register	2006
15	Force Multiple Coils	Modbus Force Multiple Coils	2015
16	Preset Multiple Registers	Modbus Preset Multiple Registers	2016

To use the functions, copy the modules into the SoftPLC7 project directory and create an entry in the SoftPLC7.ini file for any HLL-Function out of the SoftPLC7 Modbus.dll that substitutes the corresponding FC.

Example:

[HLL-Functions] 
FC2001=SoftPLC7Modbus,ModbusReadCoilStatus.

All functions got the OUT-Parameter status to indicate the progress or error condition when called or executed.
Some parameters need a broader data type to make input easier.
I.E. on registers the type DINT is used instead of WORD that allows writing “L#40001” instead of “W#16#9C41”.

Interface definitions for Modbus-Systems

At present only communication via serial interface is possible; Modbus-TCP is planed at a later date.
It is possible to use more COM-Ports, with anyone is part of a different network of Modbus-Master and several Modbus-Slaves.
The connections are defined in the SoftPLC7.ini. file

Example:

[Modbus]
MasterCount=2
Master1=(2;COM1;5;n;8;1)
Master2=(129;COM2;6;n;8;1)

Initialising of a Modbus-System

To use the Modbus-Master functions, the Master= and Slave-Parameters must be defined in advance.
The following functions are available to be placed in one of the starting OBs (100, 101, 102).

Description	HLL-Function withinSoftPLC7 Modbus.dll	FC-Number
Initialisation of a Modbus-Master	InitModbusMaster	2100
Initialisation of aModbus-Slave	InitModbusSlave	2101

The function 'InitModbusMaster' must be called with the parameter 'Intern=TRUE', that defines the SoftPLC7 as the Modbus-Master within that Modbus-System.
Parameter 'MasterID' is merely used for identification and must differ from any SlaveID.

InitModbusMaster

Interface	Parameter Name	Range	Description
IN BOOL	Internal	FALSE TRUE	Defines SoftPLC7 as a MASTER
IN INT	MasterID	1 … 255	Unique ID, other modules refer to
IN DINT	Timeout	1 … 65535	Timeout (ms) on send/receive telegrams
OUT WORD	Status		Result of executing a function

For any Modbus-Slave to communicate with, the function InitModbusSlave must be called up once.
The Offsets relate to the special Modbus-Functioncodes and may be set to 0, typical offsets are 1, 10001, 40001 and 30001.

InitModbusSlave

Interface	Parameter Name	Range	Description
IN INT	MasterID	1 … 255	MasterID the Slave belongs to
IN INT	SlaveID	1 … 255	Unique ID, other modules refer to
IN DINT	OffsetCoils	1 … 65535	Register-Offset for functioncode 1, 5, 15 (i.E. 1)
IN DINT	OffsetInFlags	1 … 65535	Register-Offset for functioncode 2 (i.E. 10001)
IN INT	OffsetHoldRegs	1 … 65535	Register-Offset for functioncode 3, 6, 16(i.E. 40001)
IN DINT	OffsetInRegs	1 … 65535	Register-Offset for functioncode 4(i.E. 30001)
OUT WORD	Status		Result of executing a function

Communication Modules

ModbusReadCoilStatus

Interface	Parameter Name	Range	Description
IN DINT	Channel	0… 65535	ID to identify a function call up
IN INT	Master ID	1 … 255	ID of Master sending the telegram
IN INT	SlaveID	1 … 255	ID of addressed Slave
IN DINT	RegFrom	0 … 65535	First requested Register
IN DINT	RegCount	1 … 255	No of requested Register
IN ANY	Buffer	Pointer to DB, M, E, A, P	Pointer to internal S7 memory
IN BOOL	Req	FALSE,TRUE	Starts transmitting on rising edge
OUT BOOL	Done		Tells whether mission is completed
OUT BOOL	Error		Tells whether mission failed
OUT WORD	Status		Result of the executed function

ModbusReadInputStatus

Interface	Parameter Name	Range	Description
IN DINT	Channel	0… 65535	ID to identify the function call
IN INT	Master ID	1 … 255	ID of the Master sending the telegram
IN INT	SlaveID	1 … 255	ID of the addressed Slave
IN DINT	RegFrom	0 … 65535	First requested Register
IN DINT	RegCount	1 … 255	No of requested Register
IN ANY	Buffer	Pointer to DB, M, E, A, P	Pointer to internal S7 memory
IN BOOL	Req	FALSE,TRUE	Starts transmitting on rising edge
OUT BOOL	Done		Tells whether mission is completed
OUT BOOL	Error		Tells whether mission failed
OUT WORD	Status		Result of the executed function

ModbusReadHoldingRegisters

Interface	Parameter Name	Range	Description
IN DINT	Channel	0… 65535	ID to identify the function call
IN INT	Master ID	1 … 255	ID of the Master sending the telegram
IN INT	SlaveID	1 … 255	ID of the addressed Slave
IN DINT	RegFrom	0 … 65535	First requested Register
IN DINT	RegCount	1 … 127	No of requested Register
IN ANY	Buffer	Pointer to DB, M, E, A, P	Pointer to internal S7 memory
IN BOOL	Req	FALSE,TRUE	Starts transmitting on rising edge
OUT BOOL	Done		Tells whether the mission is completed
OUT BOOL	Error		Tells whether the mission failed
OUT WORD	Status		Result of the executed function

ModbusReadInputRegisters

Interface	Parameter Name	Range	Description
IN DINT	Channel	0… 65535	ID to identify the function call
IN INT	Master ID	1 … 255	ID of the Master sending the telegram
IN INT	SlaveID	1 … 255	ID of the addressed Slave
IN DINT	RegFrom	0 … 65535	First requested Register
IN DINT	RegCount	1 … 127	No of requested Register
IN ANY	Buffer	Pointer to DB, M, E, A, P	Pointer to internal S7 memory
IN BOOL	Req	FALSE,TRUE	Starts transmitting on rising edge
OUT BOOL	Done		Tells whether the mission is completed
OUT BOOL	Error		Tells whether the mission failed
OUT WORD	Status		Result of the executed function

ModbusForceSingleCoil

Interface	Parameter Name	Range	Description
IN DINT	Channel	0… 65535	ID to identify the function call
IN INT	Master ID	1 … 255	ID of the Master sending the telegram
IN INT	SlaveID	1 … 255	ID of the addressed Slave
IN DINT	Reg	0 … 65535	Register to be written to
IN BOOL	Value	FALSE,TRUE	value to be writen
IN BOOL	Req	FALSE,TRUE	Starts transmitting on rising edge
OUT BOOL	Done		Tells whether the mission is completed
OUT BOOL	Error		Tells whether the mission failed
OUT WORD	Status		Result of the executed function

ModbusPresetSingleRegister

Interface	Parameter Name	Range	Description
IN DINT	Channel	0… 65535	ID to identify the function call
IN INT	Master ID	1 … 255	ID of the Master sending the telegram
IN INT	SlaveID	1 … 255	ID of the addressed Slave
IN DINT	Reg	0 … 65535	Register to be written to
IN WORD	Value	0 … 65535	value to be writen
IN BOOL	Req	FALSE,TRUE	Starts transmitting on rising edge
OUT BOOL	Done		Tells whether the mission is completed
OUT BOOL	Error		Tells whether the mission failed
OUT WORD	Status		Result of the executed function

ModbusForceMultipleCoil

Interface	Parameter Name	Range	Description
IN DINT	Channel	0… 65535	ID to identify the function call
IN INT	Master ID	1 … 255	ID of the Master sending the telegram
IN INT	SlaveID	1 … 255	ID of the addressed Slave
IN DINT	RegFrom	0 … 65535	First register to write to
IN DINT	RegCount	0 … 255	Number of registers to be written to
IN ANY	Buffer	Pointer to DB, M, E, A, P	Pointer to internal S7 memory
IN BOOL	Req	FALSER, TRUE	Starts transmitting on rising edge
OUT BOOL	Done		Tells whether the mission is completed
OUT BOOL	Error		Tells whether the mission failed
OUT WORD	Status		Result of the executed function

ModbusPresetMultipleRegisters

Interface	Parameter Name	Range	Description
IN DINT	Channel	0… 65535	ID to identify the function call
IN INT	Master ID	1 … 255	ID of the Master sending the telegram
IN INT	SlaveID	1 … 255	ID of the addressed Slave
IN DINT	RegFrom	0 … 65535	First register to write to
IN DINT	RegCount	0 … 127	Number of registers to be written to
IN ANY	Buffer	Pointer to DB, M, E, A, P	Pointer to internal S7 memory
IN BOOL	Req	FALSER, TRUE	Starts transmitting on rising edge
OUT BOOL	Done		Tells whether the mission is completed
OUT BOOL	Error		Tells whether the mission failed
OUT WORD	Status		Result of the executed function

Slave-Functionality

Introduction

In addition to Master-Mode, any SoftPLC7 may act as one or more Slave(s).
The initialisation modules 'InitModbusMaster' and 'InitModbusSlave' must be called analogue. The only difference: Parameter Intern=FALSE must be set to indicate the SoftPLC7 acts as one or more slave(s).
To respond to enquiries from an external Modbus-Slave it is necessary to allocate Register-Bands to internal S7-addresses within the starting OB.

Description	HLL-Function within SoftPLC7 Modbus.dll	FC-Number
Definition of a register band	AddModbusRegDef	2102

AddModbusRegDef

Interface	Parameter Name	Range	Description
IN INT	Master ID	1 … 255	ID of the Modbus-Master whose telegram should be respond to.
IN INT	SlaveID	1 … 255	ID of the Slave represented by the SoftPLC7
IN DINT	RegType	1..4	1=Coils, 2=InFlags, 3=HoldRegs, 4=InRegs according to the first four function codes
IN DINT	RegFrom	0 … 65535	First registers to define
IN DINT	RegCount	0..255 (bits) resp. 0..127 (words)	Number of registers to define
IN ANY	Buffer	Pointer to DB, M, E, A, P	Pointer to the first Register (regFrom). The definition of the length of the pointer is not evaluated
OUT WORD	Status		Result of the executed function

The ANY, parameter ‘Buffer’ defines the location of register ‘RegFrom’ within the SoftPLC7. Any further registers(RegCount –1) are joined behind. Words use 2 bytes, bits 1 byte.

1.Example:

AddModbusRegDef(MasterId=1,SlaveId=17,RegType=3,RegFrom=40100,RegCount=10,
Buffer=P#DB100.DBX30.0BYTE2,Status=MW0)

For the Slave with ID=17, belonging to the Master with ID=1, a Word-Register Band starting at DB100.DBX30.0 is defined. The register 40100 is read by DB100.DBW30, register 40101 by DB100.DBW32 a.s.o. The area defined by parameter Buffer is not large enough, but the size is not checked. Defining the registers as RegType=3 declares them as Holding-Register.

2.Example:

AddModbusRegDef(MasterId=1,SlaveId=17,RegType=2,RegFrom=10100,RegCount=10,
Buffer=P#DB100.DBX30.0BYTE2,Status=MW0)

For the Slave with ID=17, belonging to the Master with ID=1, a Bit-Register Band starting at DB100.DBX30.0 is defined. The register 10100 is read by DB100.DBB30, register 10101 by DB100.DBW31 a.s.o. Defining the registers as RegType=2 it appoints them to Functioncode 2 “ReadInputStatus”.

Status-Analysis

The value of Parameter 'Status' informs about the progress in executing an FC and in case of an error it gives further details.

An error condition is indicated by Bit 15 (Status>=0x8000).

Enquiry of the BIE-Flag: TRUE –no error, FALSE –error offers the same information.

Possible Status values in detail:

Status Value	Description
0x0000	No error occurred, the mission is accomplished or was not started.
0x0001	The data of a Master-Telegram were taken over to send; sending is in progress.
0x0002	Master waiting for response telegram.
0x0003	Master received a response telegram complete.
0x0004	Master evaluated a response telegram.
0x0005	Slave received 8 characters.
0x0006	Slave received remaining characters of a Master-Telegram.
0x0007	Slave received a complete Master-Telegram.
0x0008	Slave sends an answer telegram to a Master.
0x8000	Error when copying into a request telegram.
0x8001	Error on sending.
0x8002	Error on receiving.
0x8003	Error on copying into the answer telegram.
0x8100	Error on initialising the interface of a Master (INI-Entry).
0x8101	Error on opening a connection.
0x8102	Error on initialising a connection.
0x8200	Parameter error: Out of range.
0x8201	Error on reading an ANY-Pointer.
0x8202	Parameter ‘RegType’ error: Value out of [1,4].
0x8203	Parameter ‘RegFrom’ error: Value to low and not within the register band.
0x8204	Parameter ‘RegCount’ error: Value to high.
0x8300	Error when initialising Master: Master already initialised.
0x8301	Error when initialising Master: Master not yet initialised.
0x8302	Error when initialising Master: Slave= and Master ID identical.
0x8303	Error when initialising Slave: Slave already initialised.
0x8304	Error at communication block: Slave not yet initialised.

INI-FILES

SoftPLC7.ini

Section [HLL-Functions]

Entry	Type	Description / Example	Default
(FB \|FC \|SFB \|SFC )<num>	string	Defines the DLL-Function that replaces the Program-Module with the following syntax: <dll, function> Example FC13=MyDll, MyFunction For Modbus Communication the line should look like: `[HLL-Function]` FC2001=SoftPLC7Modbus,ModbusReadCoilStatus

Section [Modbus]

Entry	Type	Description / Example	Default
MasterCount	integer	Defines the number of the Modbus-System. The following syntax is used: <Number Modbus-System> Example MasterCount=2
Master <n>	string	Defines the communication parameter with the following syntax: (<MasterID>;COM<PortNo>; <Baudrate-Index>;<Parity>;<Databits>;<Stopbits>) BAUTRATE-index: 0=300, 1=600, 2=1200, 3=2400, 4=4800, 5=9600, 6=19200, 7=38400, 8=57600, 9=76800 PARITY: n=no parity, e=even parity, o=odd parity DATA BITS: 7 or 8 STOP BITS: 1 or 2 Example Master1=(2;COM1;5;n;8;1) Master2=(129;COM2;6;n;8;1)