Ask for help, unable to communicate with PLC via UART;

[wuccangel]

Sending "FFFFMFGT1" via UART PLC does not return a message; S7-1200 1212C DC/DC/DC 6ES7212-1AE40-0XB0; Fw 4.2.3； hope to get help, thanks，thanks，thanks Here is my code，

`#include <Windows.h> #include <stdio.h> #include <stdlib.h> #include #include <string.h> #include #include using namespace std;

int main() { HANDLE hcom = CreateFile(TEXT("COM3"),GENERIC_READ|GENERIC_WRITE,0,NULL,OPEN_EXISTING,0,NULL); if (hcom == INVALID_HANDLE_VALUE) { printf("open error \n"); }

DCB dcb;
GetCommState(hcom,&dcb);
dcb.BaudRate = 38400;
//dcb.BaudRate = 115200;
dcb.StopBits = 1;
dcb.Parity = 2;
dcb.ByteSize = 8;
//dcb.fOutX = 1;
//dcb.fInX = 1;

//dcb.fBinary =1;
//dcb.fParity = 1;
SetCommState(hcom,&dcb);

GetCommState(hcom,&dcb);

string magic = "MFGT1";
vector<char> v_ch;
for (int i = 0; i < 4; i++){
	v_ch.push_back('A');
}
v_ch.push_back('\0');
DWORD length = v_ch.size();
string pad = &v_ch[0];
pad.append(magic);
do
{
	
	COMSTAT rcs= {0};
	DWORD dwerror = 0;
	char recv_buf[100] = {0};
	DWORD rc_len = 0;
	ClearCommError(hcom,&dwerror,&rcs);
	ReadFile(hcom,recv_buf,rcs.cbInQue,&rc_len,NULL);
	if( rc_len > 0)
	{
		string buf = recv_buf;
		if(buf.find("CPU") != -1)
		{
			printf("buf = %s\n",buf.c_str());
			getchar();
		}
		printf("recv message len = %d\n",rc_len);
		printf("recv message:%s\n",recv_buf);
		for(int i=0; i < rc_len; i++)
		{
			printf("%x",recv_buf[i]);
		}
		printf("\n");		
	}
	PurgeComm(hcom,PURGE_TXCLEAR|PURGE_RXCLEAR);
	
	//Sleep(300);
}while(WriteFile(hcom,pad.c_str(),pad.length(),&length,NULL));	

CloseHandle(hcom);
return 0;

}`