AnsweredAssumed Answered

can not access Virtual Com Port in Windows

Question asked by Chinag Kuan Yi on Jul 4, 2018

Hi, All

I meet a big problem, I don't have any idea to fix it.

sdk path: SDK_2.3.0_MAPS-KS22\boards\mapsks22\usb_examples\usb_device_cdc_vcom\bm

PC OS: window 7 64bit, MCU: mks22,

I use usb_device_cdc_vcom to develop ks22 .

I want use my PC  to access virtual com port, so I write a sample code through WINDOWS API.

here is my source code on windows:


void setConfig() {
DCB dcbSerialParams = { 0 }; // Initializing DCB structure
COMMTIMEOUTS timeouts = { 0 };
dcbSerialParams.DCBlength = sizeof(dcbSerialParams);
GetCommState(hComm, &dcbSerialParams);
dcbSerialParams.BaudRate = CBR_9600; // Setting BaudRate = 9600
dcbSerialParams.ByteSize = 8; // Setting ByteSize = 8
dcbSerialParams.StopBits = ONESTOPBIT;// Setting StopBits = 1
dcbSerialParams.Parity = NOPARITY; // Setting Parity = None
//dcbSerialParams.fInX = 1;
if (!SetCommState(hComm, &dcbSerialParams))
printf("SetCommState fail!\n");

GetCommTimeouts(hComm, &timeouts);
timeouts.ReadIntervalTimeout = 0; // in milliseconds
timeouts.ReadTotalTimeoutConstant = 500; // in milliseconds
timeouts.ReadTotalTimeoutMultiplier = 0; // in milliseconds
timeouts.WriteTotalTimeoutConstant = 500; // in milliseconds
timeouts.WriteTotalTimeoutMultiplier = 0; // in milliseconds
if(!SetCommTimeouts(hComm, &timeouts))
printf("SetCommTimeouts fail!\n");



int OpenCom() {
hComm = CreateFile("\\\\.\\COM12", // for COM1OM9 only use COM1
0, // No Sharing
NULL, // No Security
CREATE_ALWAYS,// Open existing port only
0, // Non Overlapped I/O
NULL); // Null for Comm Devices

printf("Error in opening serial port\n");
return -1;
printf("opening serial port successful\n");

return 0;


void ComIO(PACKET_INFO packet_info) {
unsigned char pBuffer[7];
printf(" usize:%d\n", uBufSize);
memcpy(pBuffer, &packet_info, uBufSize);
for (int i = 0; i < uBufSize; i++)
printf("ComIO buffer %u is %d:\n", i, pBuffer[i]);


DWORD dNoOFBytestoWrite; // No of bytes to write into the port
DWORD dNoOfBytesWritten = 0; // No of bytes written to the port
dNoOFBytestoWrite = uBufSize;
printf("size of dNoOFBytestoWrite: %d\n", dNoOFBytestoWrite);
BOOL bRet = WriteFile(hComm, // Handle to the Serial port
pBuffer, // Data to be written to the port
dNoOFBytestoWrite, //No of bytes to write
&dNoOfBytesWritten, //Bytes written
if (dNoOfBytesWritten > 0)
printf("write successful\n");
printf("write fail\n");
if (bRet)
printf("write good!\n");

DWORD dwError = GetLastError();

printf("error: %d\n", dwError);




int main(){

  XXXX // give packet_info some value in here 

  OpenCom() ;




My question is when I use my sample code to access port,

open com and write com is successful, but KS22(MCU) can not receive my send data.

but I use PUTTY to access port first,  KS22 can receive my send data. after that I run my sample code, it works too.

ks22 can receive my send data through my sample code.


it seems like I need use PUTTY to open port and send data first, after that I can use my sample code to access port.

it seems like PUTTY do some communicate, that my sample code didn't do.

how can I modify my sample code, makes it work.(don't need to use PUTTY access port first)

I don't have any idea, who can help me please~