Since there is only one Chip used in the DIP40 board, there are lots of empty space. So there is a USB-TTL circuit added using CH551G. 

With the integrated USB-TTL, we can connect the Single Chip Computer to a PC using VCC, GND, D+ and D- of the USB port. We do not need a external USB-TTL circuit.

Just using VCC, GND, D+ and D- we can connect the Single Chip Computer to a PC serial terminal via USB port.  The power for Single Chip Computer and USB-TTL circuit drawn from USB port.  No external power supply required.