AN197

Rev. 0.6

7

7.1. Windows XP/2000/Server 2003/Vista

To find the port number in Windows XP/2000/Server 2003/Vista, the corresponding key listed above needs to be

opened. This is done using several registry calls using Windows API functions. The function is passed the VID,

PID, and serial number, and the return value is either the port number that the CP210x is located on, or a –1 if

there is a failure. The function below will find the CP210x port number in Windows XP/2000/Server 2003/Vista (this

function can be copied straight into application code that needs to discover the COM port number):

int GetPortNumXP2000Vista(WORD vid, WORD pid, char* ser)

{

//Variables used for Registry access

HKEY tmpKey, tmpSubKey, tmpPortKey;

CString portKeyString;

DWORD valtype;

char* portString;

DWORD length = 100;

portString = new char[101];

//Set portnum to -1, so if there is an error we will

//know by returning a negative port value

int portNum = -1;

//

Open keys to get to the key where the port number is located. This key is:

//

HKLM\System\CurrentControlSet\Enum\USB\Vid_xxxx&Pid_yyyy&Mi_00\zzzz_00\DeviceParameters\PortN

ame

if (ERROR_SUCCESS == RegOpenKeyEx(HKEY_LOCAL_MACHINE, "SYSTEM\\CurrentControlSet\\", 0,

KEY_READ, &tmpKey))

{

if (ERROR_SUCCESS == RegOpenKey(tmpKey, "Enum\\USB\\", &tmpSubKey))

{

//Loop through and replace spaces for WinXP2000Vista

int i = 0;

while (ser[i] != '\0')

{

if (ser[i] == 0x20)

ser[i] = '_';

i++;

}

//The portkey string should look like this

//"Vid_XXXX&Pid_XXXX&MI_00\\XXXX_00" where the XXXX's are Vid, Pid and serial string

- version less than 5.0

//"Vid_XXXX&Pid_XXXX\\XXXX" where the XXXX's are Vid, Pid and serial string -

version greater than or equal to 5.0

portKeyString.Format("Vid_%04x&Pid_%04x&Mi_00\\%s_00\\Device

Parameters\\",

vid,

pid, ser);

//If the portkey string is in the registry, then go ahead and open the portname

if

(ERROR_SUCCESS

==

RegOpenKeyEx(tmpSubKey,

portKeyString,

0,

KEY_READ,

&tmpPortKey))

{

if (ERROR_SUCCESS == RegQueryValueEx(tmpPortKey, "PortName", NULL, &valtype,

(unsigned char *)portString, &length))

{

// When we obtain this key, it will be in string format of

// "COMXX" where XX is the port. Simply make the first three

// elements of the string 0, and call the atoi function to obtain

// the number of the port.