Downloader and the light cubic connection:
GND to GND
5v or VCC to 5v or VCC
RXD to RXD
TXD to TXD

Because the light cubic current will affect the downloader, so the 5V line that does not take directly with the power supply line, when downloadding the need to cold start the microcontroller (
Meaning that the microcontroller needs to power off and then re-power to download), the power switch as a cold start on the line, the downloader device connected to the computer, need to disconnect the switch
Re-power can be downloaded, the host computer connection is the same way, with the power line directly power supply.
