Multiplexing technique is based on the idea of Persistence of vision of the human eyes. The sample schematic of 3 digits multiplexing is shown below. Segment a-g of each digit are connected together. Each digit is switched on-off by controlling signal at Digit 1, Digit 2 and Digit 3. For example, if Digit 1 is '1' , Digit 1 will be on. If Digit 1 is '0', Digit 1 will be off. People will see all 3 digits display in the same time if each digit switch on and off fast enough.
By using multiplexing technique the number of required connections for 6 digits display is reduced from 42 pins to 7-Segment+6 digits = 13 pins Wow!! I can drive 6 digits 7-segment display by using just a PIC16F627A.
Next time, I will post the program for LED 7-Segment Multiplexing
--- Updated 21 Dec 2008 --
The program for LED 7-Segment Multiplexing is now posted at 6 Digits LED 7-Segment Multiplexing