Modbus TCP源代码-编程举例
一个TCP/IP主机是Modbus/TCP读取寄存器的源代码，只需修改TCP/IP的接口部分就可以在以下环境下使用：
1. 命令行的JAVA应用程序
2. UNIX下基于命令行的C应用程序
3. Win32下基于命令行的C应用程序
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
// 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("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); // 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=0;i<5;i++) 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;
tcpip详解 源代码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=0;i<num_regs;i++)
{
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;
}

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