The stc-isp burning program for 51 single chip microcomputer always shows that "the target single chip microcomputer is being detected..." the cold start board does not respond

1、 In this case, it may be the board and computer USB Poor serial port contact , If you order STC—ISP Without moving , Can be taken off STC—ISP After reopening, solve . If it's too much trouble, you can pull out the plug on the board USB Just plug in again .
2、 If the above methods cannot be solved , It may be because the jumper cap is improperly connected , Or bad , The correct connection is ：TXD and RXD Wrong connection , Downloader TXD Connect to MCU RXD,RXD Connect to MCU TXD.
3、 There are still some problems ： The crystal oscillator is not inserted or loose .
4、 The model of single chip microcomputer is wrong , If it is STC89c52RC It is necessary to add RC Of ,STC89c52 No way. .