串口读写不一致

void Thread::GetSensorState()
{
    int i,wlen,rlen;
    char command='\0';
    char txbuff[6];
    char revbuff[7];
    QByteArray rev = " ";
    for(command=0x10;command<=0x20;command++)
    {
            //printf("\n command:%#x",command);
            if( (command == 0x1b)| (command == 0x1c) )
                continue;
            memset(txbuff,'\0',sizeof(txbuff));
            txbuff[0]=0xAA;
            txbuff[1]=0xFF;
            txbuff[2]=command;
            txbuff[3]=0xFF;
            txbuff[3]= txbuff[3]^txbuff[2];
            txbuff[4]=0xFF;
            txbuff[5]='\0';
            fflush(stdout);
            wlen = m_tty.tty_write(sel_fd,txbuff,6);
            fflush(stdout);
            memset(revbuff,'\0',sizeof(revbuff));
            rlen = m_tty.tty_read(sel_fd,revbuff,7);
            fflush(stdout);
            if(rlen < 0)
            {
                printf("read serial error!\n");
                rlen = m_tty.tty_read(sel_fd,revbuff,7);      
            }
            rev = " ";
            for(i=2;i<4;i++)
                rev.append(revbuff[i]);
            char str[3]= {'\0'};
            char value = '\0';  //
            char *temp = rev.data();
            i=0;
            for(i=0;i<3;i++){
                str[i]= *temp;
                temp++;
            }
            value = (str[1] << 4)|str[2];
            char d[2] = {'\0'};
            sprintf(d,"%x",value);
            for(i=2;i<5;i++)
            {
              printf(" %x",revbuff[i]);
            }
            revbuff[6]=0;
            for(i=2;i<4;i++)
            {
                revbuff[5]=revbuff[5]^revbuff[i];
            }
            switch(txbuff[2])
            {
                case 0x10:
                    sensor_ui->LE_Temperature->setText(QString(d));
                    break;
                case 0x1D:
                    sensor_ui->LE_Humidity->setText(QString(d));
                    break;
            }
        }
}

各位好，这段代码是读串口数据的代码，但是读出来的数跟写进去的不一样，哪位大侠可以帮忙看一下，能不能改成写的跟读的一样，小弟不胜感激。