modbusclient.h

Convert Interface on a embedded System

#pragma once

#include "ModbusConnection.h"

// Modbus function codes for supported requests (see Modbus Protocol Specification)
#define MODBUS_READ_REGS    3	// Read Multiple Registers
#define MODBUS_WRITE_REGS  16	// Write Multiple Registers

// Modbus exception codes (see Modbus Protocol Specification)
#define ILLEGAL_FUNCTION  1
#define ILLEGAL_ADDRESS   2
#define ILLEGAL_VALUE     3

// Max allowed request quantities (see Modbus Protocol Specification)
#define MAX_READ_REGS  125  // Max for Read Multiple Registers
#define MAX_WRITE_REGS 100  // Max for Write Multiple Registers

// Modbus/TCP constants (see Modbus/TCP Protocol Specification)
#define LEN_HEADER 7	// Length (bytes) of MBAP Header
#define LEN_DESTID 1	// Length (bytes) of 'Destination ID' field of MBAP Header
#define LEN_MINPDU 1	// Length (bytes) of shortest valid PDU
#define LEN_MAXPDU 253  // Length (bytes) of longest valid PDU [see note below]

/*
 * Modbus/TCP Spec states a max PDU length of 249 bytes.  However, 
 * in order to support the well documented max request quantity
 * of 125 registers for Modbus Function Code 03 (Read Multiple 
 * Registers), it's necessary to maintain the same max PDU 
 * (not ADU) as serial-line implementations, which is 253 bytes.
 */

// Arbitrary number of 'Registers' for the data area
#define N_REGISTERS 30

#define LEN_MAXADU (LEN_HEADER + LEN_MAXPDU)


// Modbus REQUEST structure used by this module
typedef struct tagREQUEST
{
    BYTE  bFnCode;	// Modbus Function Code of request
    WORD  wAddr;	// Address of first 'Register' to read (or write)
    WORD  wQty;		// Quantity of 'Registers' to read (or write)
    WORD  awData[MAX_READ_REGS];  // The data values read (or to be written)
}REQUEST, *LPREQUEST;

class CModbusClient
{
public:
	CModbusClient(void);
	~CModbusClient(void);

	void StartClientThread( HANDLE hConn);

	static WORD ReceiveRequest( SOCKET socket, LPBYTE buffer, LPWSAOVERLAPPED lpOverlap, HANDLE hStop );
	static BOOL ReceiveBytes( SOCKET socket, LPWSABUF lpBuffer, LPWSAOVERLAPPED lpOverlap, HANDLE hStop );
	static WORD ParseHeader( LPBYTE buffer );
	static BYTE ParseRequest( LPBYTE buffer, WORD wRecv, LPREQUEST lpRequest );
	static BYTE ProcessRequest( LPREQUEST lpRequest );
	static WORD MakePositiveResponse( LPREQUEST lpRequest, LPBYTE buffer );
	static WORD MakeErrorResponse( BYTE bError, BYTE bFnCode, LPBYTE buffer );
	static BOOL SendResponse( SOCKET socket, LPBYTE buffer, WORD nBytesToSend );
	static BOOL SetRegisters( int iStart, int nQty, LPWORD lpData );
	static BOOL GetRegisters( int iStart, int nQty, LPWORD lpData );

};