What is the principle of digital tube controlled by 51 microcontroller?

Digital tube is actually composed of light-emitting diodes, there are *** cathode and *** anode, for *** anode, a digital tube consists of 8 diodes, their anodes are connected together to the +5v power supply, and the cathodes are connected to a port, such as the p1 of the 8 pins, when a pin outputs a low level of digital tube diode corresponding to the bright.

Question added:

Because the human eye has a hysteresis, if you give a digital tube connected to 0.3 seconds, and then another connected to 0.3 seconds, and constantly give several digital tube turns connected to 0.3 seconds, because of the hysteresis of the human eye, the number of the display you require, of course, the specific connection time, depending on the number of digital tubes and other circumstances of their own adjustments.