串行口的简单问题,求救

[Hercule]

if(m_hCom == INVALID_HANDLE_VALUE)
{
m_hCom=CreateFile(m_name,GENERIC_READ | GENERIC_WRITE,
0,
NULL,
OPEN_EXISTING,
FILE_ATTRIBUTE_NORMAL,
NULL);
if(m_hCom == INVALID_HANDLE_VALUE)
return false;
}

GetCommState(m_hCom, &dcb);
dcb.BaudRate=115200;
dcb.ByteSize=8;
dcb.Parity=2;
dcb.StopBits=1;
int jj = SetCommState(m_hCom, &dcb);
jj = GetCommState(m_hCom,&dcb);

上面的代码中,调用SetCommState总是失败(jj返回0),但是把dcb.StopBits改为0就可
成功,这是为什么啊?