modbus tcp 协议的c语言怎么写

如果用C语言编程实现MODBUS通讯，难度还是很大的。首先需要实现TCP通讯，这里面涉及到TCP侦听模块、TCP数据收发模块、断线重连模块、如果是多信道连接，还需要处理多信道并行通讯等。在实现了TCP通讯核心程序的基础上，通过数据发送程序模块，按照MODBUS指令格式，向前端设备发出正确的MODBUS指令（RTU或ASCII）即可，然后就是通过数据接收模块等待接收前端返回的MODBUS数据包，这就还要编写MODBUS指令生成模块，MODBUS数据解析模块。

上述只是一个大致的思路，散誉猜里面涉及的虚兆编程技术很多，有的技术环节还是很有挑战性的，比如大规模多信道并行通冲型讯。

test1.cpp

-

Win32

console

app

to

read

registers

//

test1.cpp

5/23/97

//

example

Win32

C++

program

to

read

registers

from

PLC

via

gateway

//

compile

with

BC45

or

BC50

/郑森/

default

settings

for

Win32

console

app

//

empty

DEF

file

#include

<winsock.h>

#include

<stdio.h>

#include

<conio.h>

int

main(int

argc,

char

**argv)

{

if

(argc<5)

{

printf("喊携亩usage:

test1

ip_adrs

unit

reg_no

num_regs\n"

"eg

test1

198.202.138.72

5

0

10\n")

return

1

}

char

*ip_adrs

=

argv[1]

unsigned

short

unit

=

atoi(argv[2])

unsigned

short

reg_no

=

atoi(argv[3])

unsigned

short

num_regs

=

atoi(argv[4])

printf("ip_adrs

=

%s

unit

=

%d

reg_no

=

%d

num_regs

=

%d\n",

ip_adrs,

unit,

reg_no,

num_regs)

//

initialize

WinSock

static

WSADATA

wd

if

(WSAStartup(0x0101,

&wd))

{

printf("cannot

initialize

WinSock\n")

return

1

}

//

set

up

socket

SOCKET

s

s

=

socket(PF_INET,

SOCK_STREAM,

IPPROTO_TCP)

struct

sockaddr_in

server

server.sin_family

=

AF_INET

server.sin_port

=

htons(502)

//隐核

ASA

standard

port

server.sin_addr.s_addr

=

inet_addr(ip_adrs)

int

i

i

=

connect(s,

(sockaddr

*)&server,

sizeof(sockaddr_in))

if

(i<0)

{

printf("connect

-

error

%d\n",WSAGetLastError())

closesocket(s)

WSACleanup()

return

1

}

fd_set

fds

FD_ZERO(&fds)

timeval

tv

tv.tv_sec

=

5

tv.tv_usec

=

0

//

wait

for

permission

to

send

FD_SET(s,

&fds)

i

=

select(32,

NULL,

&fds,

NULL,

&tv)

//

write

if

(i<=0)

{

printf("select

-

error

%d\n",WSAGetLastError())

closesocket(s)

WSACleanup()

return

1

}

//

build

request

of

form

0

0

0

0

0

6

ui

3

rr

rr

nn

nn

unsigned

char

obuf[261]

unsigned

char

ibuf[261]

for

(i=0i<5i++)

obuf[i]

=

0

obuf[5]

=

6

obuf[6]

=

unit

obuf[7]

=

3

obuf[8]

=

reg_no

>>

8

obuf[9]

=

reg_no

&

0xff

obuf[10]

=

num_regs

>>

8

obuf[11]

=

num_regs

&

0xff

//

send

request

i

=

send(s,

obuf,

12,

0)

if

(i<12)

{

printf("failed

to

send

all

12

chars\n")

}

//

wait

for

response

FD_SET(s,

&fds)

i

=

select(32,

&fds,

NULL,

NULL,

&tv)

//read

if

(i<=0)

{

printf("no

TCP

response

received\n")

closesocket(s)

WSACleanup()

return

1

}

//

read

response

i

=

recv(s,

ibuf,

261,

0)

if

(i<9)

{

if

(i==0)

{

printf("unexpected

close

of

connection

at

remote

end\n")

}

else

{

printf("response

was

too

short

-

%d

chars\n",

i)

}

}

else

if

(ibuf[7]

&

0x80)

{

printf("

Modbus

exception

response

-

type

%d\n",

ibuf[8])

}

else

if

(i

!=

(9+2*num_regs))

{

printf("incorrect

response

size

is

%d

expected

%d\n",i,(9+2*num_regs))

}

else

{

for

(i=0i<num_regsi++)

{

unsigned

short

w

=

(ibuf[9+i+i]<<8)

+

ibuf[10+i+i]

printf("word

%d

=

%d\n",

i,

w)

}

}

//

close

down

closesocket(s)

WSACleanup()

return

0

}

刚好我在弄crc校验拍运宏悄腔。给你一段代码。我也是冲网上抄过袭册来的。验证过了。

unsigned short crc16

static uchar code auchCRCHi[256] = {

0x00, 0xC1, 0x81, 0x40, 0x01, 0xC0, 0x80, 0x41, 0x01, 0xC0,

0x80, 0x41, 0x00, 0xC1, 0x81, 0x40, 0x01, 0xC0, 0x80, 0x41,

0x00, 0xC1, 0x81, 0x40, 0x00, 0xC1, 0x81, 0x40, 0x01, 0xC0,

0x80, 0x41, 0x01, 0xC0, 0x80, 0x41, 0x00, 0xC1, 0x81, 0x40,

0x00, 0xC1, 0x81, 0x40, 0x01, 0xC0, 0x80, 0x41, 0x00, 0xC1,

0x81, 0x40, 0x01, 0xC0, 0x80, 0x41, 0x01, 0xC0, 0x80, 0x41,

0x00, 0xC1, 0x81, 0x40, 0x01, 0xC0, 0x80, 0x41, 0x00, 0xC1,

0x81, 0x40, 0x00, 0xC1, 0x81, 0x40, 0x01, 0xC0, 0x80, 0x41,

0x00, 0xC1, 0x81, 0x40, 0x01, 0xC0, 0x80, 0x41, 0x01, 0xC0,

0x80, 0x41, 0x00, 0xC1, 0x81, 0x40, 0x00, 0xC1, 0x81, 0x40,

0x01, 0xC0, 0x80, 0x41, 0x01, 0xC0, 0x80, 0x41, 0x00, 0xC1,

0x81, 0x40, 0x01, 0xC0, 0x80, 0x41, 0x00, 0xC1, 0x81, 0x40,

0x00, 0xC1, 0x81, 0x40, 0x01, 0xC0, 0x80, 0x41, 0x01, 0xC0,

0x80, 0x41, 0x00, 0xC1, 0x81, 0x40, 0x00, 0xC1, 0x81, 0x40,

0x01, 0xC0, 0x80, 0x41, 0x00, 0xC1, 0x81, 0x40, 0x01, 0xC0,

0x80, 0x41, 0x01, 0xC0, 0x80, 0x41, 0x00, 0xC1, 0x81, 0x40,

0x00, 0xC1, 0x81, 0x40, 0x01, 0xC0, 0x80, 0x41, 0x01, 0xC0,

0x80, 0x41, 0x00, 0xC1, 0x81, 0x40, 0x01, 0xC0, 0x80, 0x41,

0x00, 0xC1, 0x81, 0x40, 0x00, 0xC1, 0x81, 0x40, 0x01, 0xC0,

0x80, 0x41, 0x00, 0xC1, 0x81, 0x40, 0x01, 0xC0, 0x80, 0x41,

0x01, 0xC0, 0x80, 0x41, 0x00, 0xC1, 0x81, 0x40, 0x01, 0xC0,

0x80, 0x41, 0x00, 0xC1, 0x81, 0x40, 0x00, 0xC1, 0x81, 0x40,

0x01, 0xC0, 0x80, 0x41, 0x01, 0xC0, 0x80, 0x41, 0x00, 0xC1,

0x81, 0x40, 0x00, 0xC1, 0x81, 0x40, 0x01, 0xC0, 0x80, 0x41,

0x00, 0xC1, 0x81, 0x40, 0x01, 0xC0, 0x80, 0x41, 0x01, 0xC0,

0x80, 0x41, 0x00, 0xC1, 0x81, 0x40

}

// CRC 低位字节值表

static uchar code auchCRCLo[256] = {

0x00, 0xC0, 0xC1, 0x01, 0xC3, 0x03, 0x02, 0xC2, 0xC6, 0x06,

0x07, 0xC7, 0x05, 0xC5, 0xC4, 0x04, 0xCC, 0x0C, 0x0D, 0xCD,

0x0F, 0xCF, 0xCE, 0x0E, 0x0A, 0xCA, 0xCB, 0x0B, 0xC9, 0x09,

0x08, 0xC8, 0xD8, 0x18, 0x19, 0xD9, 0x1B, 0xDB, 0xDA, 0x1A,

0x1E, 0xDE, 0xDF, 0x1F, 0xDD, 0x1D, 0x1C, 0xDC, 0x14, 0xD4,

0xD5, 0x15, 0xD7, 0x17, 0x16, 0xD6, 0xD2, 0x12, 0x13, 0xD3,

0x11, 0xD1, 0xD0, 0x10, 0xF0, 0x30, 0x31, 0xF1, 0x33, 0xF3,

0xF2, 0x32, 0x36, 0xF6, 0xF7, 0x37, 0xF5, 0x35, 0x34, 0xF4,

0x3C, 0xFC, 0xFD, 0x3D, 0xFF, 0x3F, 0x3E, 0xFE, 0xFA, 0x3A,

0x3B, 0xFB, 0x39, 0xF9, 0xF8, 0x38, 0x28, 0xE8, 0xE9, 0x29,

0xEB, 0x2B, 0x2A, 0xEA, 0xEE, 0x2E, 0x2F, 0xEF, 0x2D, 0xED,

0xEC, 0x2C, 0xE4, 0x24, 0x25, 0xE5, 0x27, 0xE7, 0xE6, 0x26,

0x22, 0xE2, 0xE3, 0x23, 0xE1, 0x21, 0x20, 0xE0, 0xA0, 0x60,

0x61, 0xA1, 0x63, 0xA3, 0xA2, 0x62, 0x66, 0xA6, 0xA7, 0x67,

0xA5, 0x65, 0x64, 0xA4, 0x6C, 0xAC, 0xAD, 0x6D, 0xAF, 0x6F,

0x6E, 0xAE, 0xAA, 0x6A, 0x6B, 0xAB, 0x69, 0xA9, 0xA8, 0x68,

0x78, 0xB8, 0xB9, 0x79, 0xBB, 0x7B, 0x7A, 0xBA, 0xBE, 0x7E,

0x7F, 0xBF, 0x7D, 0xBD, 0xBC, 0x7C, 0xB4, 0x74, 0x75, 0xB5,

0x77, 0xB7, 0xB6, 0x76, 0x72, 0xB2, 0xB3, 0x73, 0xB1, 0x71,

0x70, 0xB0, 0x50, 0x90, 0x91, 0x51, 0x93, 0x53, 0x52, 0x92,

0x96, 0x56, 0x57, 0x97, 0x55, 0x95, 0x94, 0x54, 0x9C, 0x5C,

0x5D, 0x9D, 0x5F, 0x9F, 0x9E, 0x5E, 0x5A, 0x9A, 0x9B, 0x5B,

0x99, 0x59, 0x58, 0x98, 0x88, 0x48, 0x49, 0x89, 0x4B, 0x8B,

0x8A, 0x4A, 0x4E, 0x8E, 0x8F, 0x4F, 0x8D, 0x4D, 0x4C, 0x8C,

0x44, 0x84, 0x85, 0x45, 0x87, 0x47, 0x46, 0x86, 0x82, 0x42,

0x43, 0x83, 0x41, 0x81, 0x80, 0x40

}

//CRC校验的函数

unsigned short CRC16(unsigned char *puchMsg, unsigned short usDataLen)

{

unsigned char uchCRCHi = 0xFF /* 高CRC字节初始化 */

unsigned char uchCRCLo = 0xFF /* 低CRC 字节初始化 */

unsigned uIndex /* CRC循环中的索引 */

while (usDataLen--) /* 传输消息缓冲区 */

{

uIndex = uchCRCHi ^ *puchMsg++ /* 计算CRC */

uchCRCHi = uchCRCLo ^ auchCRCHi[uIndex]

uchCRCLo = auchCRCLo[uIndex]

}

return (uchCRCHi <<8 | uchCRCLo)

}

调用方式：dd=CRC16(tmp,x)；

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