1. This is an example of a 4-digit cc-type 7-segment multiplexed display system.
Figure-1: Example of 4-digit multiplexed display system
2. In this multiplexed display system, there is only one 8-bit data path (PD7-PD6 PB5-PB0) over which 4 different signals (0x06 -- cc-code for 1; 0x5B -- cc-code for 2; 0x4F -- cc-code ofr 3; 0x66 -- cc-code for 4) travel at different times for 4 different destinations which are DP0 (display position 0), DP1, DP2, and DP3.
3. When 1 appears at DP0 position, there are nothing on DP1-DP3 positions (they remain completely blank); when 2 appears at DP1 position, there are nothing on DP0, DP2-DP3 positions (they remain completely blank) and so on. There is only one digit that is present/visible on the display system at one time.
4. If the statement of Step-3 is true (and it is true), then what do we do to see all the digits (1234) on the display system at a time? The trick is (also see Fig-2 in Step-6):
We maintain a walking 0 (logic-low) across the cc-pins (cc0, cc1, cc2, and cc3) of the display units. The speed of this 'walking 0' is about 100 kHz. We call this speed the 'scan frequency'. I had not heard that anybody was saying it 'sweep' or 'sweep frequency' -- a term used in 'television technology'.
The 'scanning technique' does not create the 'illusion' for us to see all the digits simultaneously; rather, it is the 'eye perception' by virtue of which we see that all the digits are there. The eye saw digit 1 at DP0 position at time t1; at time t2, the digit 1 has gone from its position and a new digit 2 has arrived at position DP1. The eye sees both digits (1, 2) as the eye has not yet forgotten what it saw a while ago. We can decrease the 'scan frequency' and doing so we can force the eye to loss its 'perception power'. Now, the eye will see only the digit 2.
Every field of disciple has it own set of vocabulary that regulates our communications. For example: in hardware what we call data, that is called streams in software. Arduino Forum is predominantly a hardware platform; software (particularly the Library Functions) has come as a great aid to program it. Unfortunately, some of the software veterans talk in a very high level of 'abstraction'.
5. In a multiplexed display system, scanning is done on all the cc-pins of the display units whether there is any data or not for a display position. For example: we want to show only 4 at DP3 position of Fig-1; as a result, there is only one digit that is ON for all the time. Is it going to cause over-heating for the segments of the digit 4? No! The average current for each segment is independently same, which is controlled by the 'series current limiting resistor (2.2K).
6. Multiplexing Mechanism of 16-digit Display System (direct driven without any display controller) of a Taxi Meter (6-digit Fare Meter, 6-digit Distance Meter, and 4-digit Waiting Time Meter)
Figure-2: 16-digit direct driven multiplexed display system