labwindows/CVI ComRd卡

串口收发数据，结果在读数据的时候卡了，卡在了ComRd处，请问是为什么？

int CVICALLBACK tt (int panel, int control, int event,
                    void *callbackData, int eventData1, int eventData2)
{
    int Byte_send;
    int Strlen;
    unsigned char ReadBuf[20]={0};
    unsigned char Receive[9]={0};
    double weiyi;
    
    int ReceiveData=0;
    switch (event)
    {
        case EVENT_TIMER_TICK:
            FlushInQ(6);
            FlushOutQ(6);
            Byte_send=ComWrt(6,Write,8);
            //Strlen=GetInQLen(6);
            ComRd(6,ReadBuf,20);
            for(int i=0;i<9;i++)
            {
                Receive[i]=ReadBuf[i+5];
            }
            sprintf(Receive,"%c%c%c%c%c%c%c",Receive[0],Receive[1],Receive[3],Receive[4],Receive[5],Receive[6],Receive[7]);
            weiyi=atof(Receive);
            SetCtrlVal(panelHandle,PANEL_NUMERICMETER,weiyi);
            FlushInQ(6);
            FlushOutQ(6);
            break;
    }
    return 0;
}

定时器设置为1秒，发送正常，接收的时候能卡5-10秒才收到数，函数参考NI的例程，为什么会出现卡的问题？