How to know the scan mode of led display?

What does the Scanning Drive of LED screen mean?

General introduction

Scanning Drive or Multiplexing is one of the methods of the led module design. It`s about the amount of LEDs that is connected with ONE chip leg.
    There are design techniques that will made it possible to connect more LEDs on ONE chip leg. Most suppliers will have 1/2, 1/4, 1/8, 1/16 and 1/32 scan.
    Scanning Drive will reduce brightness of the led screen and in most cases they will use it on a higher resolution for brightness compensation.
The higher resolution = higher brightness and higher scan = lower brightness
    Most scanning Drive will be used on indoor led screen since brightness is not an issue (exception PH10 and PH12 Outdoor and …) and will also be used when there is not enough place for the PCB.  
 
 

Driving Mode

Driving mode includes static mode and dynamic mode.
As we know that each LED lamp on module is actually connected with one pin of driving IC, connecting one or several lamps with the pin/s will come to different ways of the driving mode, one is Static constant current mode, the other is Dynamic san mode, below images show the connection of LED lamp in static mode and dynamic mode.
 

 From the above schematic diagram of static constant mode, we can see that a led lamp is only connected with one pin only, the signal a LED lamp receives from driving IC is through one pin only. It is fixed and unchanged, so we called it static constant current.
In static constant current, the signal (digital signal or current signal) received by a led lamp is 100% from the driving IC through pin, so the brightness is highest; such driving mode is commonly adopted by outdoor LED screen.
From the above schematic diagram of dynamic mode, we can see that four led lamps are connected with one pin, the signal from driving IC through pin is shared by four led lamps, each led lamp shares one fourth of the whole signal, we called it 1/4 scan, but here we need to know is that the signal shared by four led lamps sometimes evenly, sometimes not, it is not fixed and changeable, so we called it dynamic scan.
In LED screen driving mode of dynamic scan, the signal may be shared by two led lamps, four led lamps, eight led lamps, then we have 1/2 scan, 1/4 scan, 1/8 scan.

What purpose of static mode and dynamic mode?

From above analysis, we can conclude that when each LED lamp is connected with pin driving IC, the more led lamps share the signal (power and data), the brightness will be higher, but for indoor LED screen (P3,…,PH10)and high resolution outdoor LED screen (PH10 and PH12), we should change driving mode to have reasonable and suitable brightness to meet the actual purpose, for example, PH16 outdoor LED screen(3906 pixels/m2) by static mode will reach brightness over 8000 nits, but if we use same driving mode for PH12 outdoor LED screen (6944 pixels/m2), the brightness will be surely over 15000 nits, but as know that outdoor brightness requirement is only around 6500 nits, so it is definitely not necessary to use static mode on PH12 LED screen, so we normally use 1/2 scan mode, its brightness will be around 7500 nits, but if you use 1/4 scan mode, its brightness will be less than 5000 nits, which may not enough for outdoor advertising purpose, especially when LED screen is to against strong sunshine.
Now we know that we choose different types of scan modes to change the brightness to suit the practical use, such as 1/2 scan, 1/4 scan, 1/8 scan, even 1/16, 1/32 and normally in brightness comparison: 1/2 scan> 1/4 scan>1/8 scan> 1/16, but LED screen resolution should be also considered.

What is scan mode? 

LED screen scan mode definition: in a LED screen area, and light the number of rows and rows of whole area ratio.
1. Indoor single color: plain 1/16 scan
2. Indoor full color: is generally 1/8 scanning
3. Outdoor single color: is generally 1/4 scanning
4. Outdoor full-color: is generally static scan
To illustrate: a commonly used fullcolor module for 168 pixels (2R1G1B ), if mbi5026 driving, module use a total of LED number is:168* ( 2+1+1 ) =512, mbi5026 16 bit chip, 512/16=32.
In the LED unit board, scanning modes are 1/16, 1/8, 1/4, 1/2, static. One of the most simple way is to count the unit board LED number and 74HC595 number.
Calculation method of dividing the number: LED 74HC595 8= number divided by a fraction of a scanning.
General indoor LED screen, now general control method uses the ranks of control mode, namely scanning mode, at present LED electronic screen driving mode includes scanning static and dynamic scanning two, static scan is divided into static real pixel and static virtual, dynamic scanning is also divided into dynamic image and dynamic virtual; in LED electronic display, and light the number of rows and rows of whole area ratio, called the LED screen scanning mode. While scanning is also 1/2 scan, 1/4 scan, 1/8 scan, 1/16 and several drive modes. That said display driver is not the same, then the card receiving set is not the same. If the receiving card was used in 1/4 scanning screen, now used in a static screen, then on the display will be every 4 on line. General reception card set, connected to send a card, display, computer and other major components, can be in the computer into the associated software settings.

How does the LED Screen Scan Mode work?

Here give you detail information:

                                            
                                      
This means LED screen is driven by IC          This means LED screen is off
Each drive IC have 16 pins, and can drive 16 LED chip at the most. Static drive mode means all the LEDs on the LED module are driven by IC at any time, like following image: 

1/12 scan mode, means 1/12 LEDs on the module are driven by IC at one time, and next time there are other 1/12 LEDs are driven.
 

 

1/6 scan mode, means 1/6 LEDs on the module are driven by IC at one time, and next time there are other 1/6 LEDs are driven.

Note: Because the LED screen scan mode change scan lines very fast, and can’t be distinguished by human eyes, so in visually, we feel the LEDs are light on all the time, but in fact, the scan mode have LEDs off when we see it.

What’s the effect of scan mode for LED screen?

1) Brightness: The high scan with more LEDs light on at one time, so the brightness are higher than lower scan mode, in theory, for the same LED screen, static scan is double brightness of 1/2 scan, and 1/4 scan is double brightness of 1/8 scan. But this is not absolute formula, because sometime there don’t need so much brightness, and will low down the current, and finally cut the brightness.
2) Refresh rate: Usually lower scan with lower refresh rate than the higher scan. And this is not applicable like the multiple formula as brightness, because the refresh rate mainly depend on the PCB design.
3) Power consume: In theory, the higher scan, the higher power, this is applicable multiple formula, for example 1/5 scan is double power consume of 1/10 scan. Also, it restrict by the current, factories may reduce current and finally reduce power and brightness.
Therefore, it’s very important to choose a reasonable scan mode for LED screen, not the higher the better, also not converse. It need based on the brightness, power, refresh rate and cost, finally design a good LED screen.

What is Driving IC?

Driving IC is an integrated electronic component, which is mounted in the surface of PCB (back side of module), the driving IC receives and sends data signal and power signal to LED lamp through integrated circuit on PCB.
Driving IC for outdoor led screen normally has 24 pins, among 24 pins of driving ICs as the right picture shows, 16(5th-20th) of 24 pins control led lamp and each pin controls one led lamp only, another 8 of 24 pins for other purposes, as below image shows:

 

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How to know the scan mode of led display?

As a frequently mentioned professional terms, "scan mode", also called as "driving method", sometimes makes the beginners or even the experienced clients feel confused. In fact it's not so hard to understand. For example of 1/4 driving led display, you could simply imagine that at one moment, only 1/4 of the LEDs are driven on by the driving IC. Certainly it's hard to sense it by human eyes, but the professional cameras, when we set which at very high shutter speed, it is possible to capture it. The exist of scan mode 1/4, 1/8, 1/16 etc is reasonable, because sometimes we don't need very high brightness, very high refresh frequency, and sometimes we need to reduce the power consumption as well as the cost...but in this article, we're not introducing the details of this concept, or analyzing its reason why. Instead, we're introducing "how to know the scan mode" of led display when you see one LED module in hand.
And yes it's very easy to work out this.
Taking an example of the P3 LED module.


You will calculate out the scan mode of this LED module in below 3 steps:
1. The total pins amount of this LED module's driving IC. From this picture can find that there are 8 small groups of LED driving IC, and each group contains 3 LED driving IC, so we would know that there are totally 8x3=24 LED driving IC;
Each LED driving IC has 16 pins;
So we would know there are totally 24x16=384 pins of LED driving IC on this LED module.
And let's record this number 384.
2. The total LED chips amount of this LED module.The resolution of this LED module is 64x32=2048 pixels, and each LED contains 3 color chips(R,G,B), so there will be totally 2048x3=6144 LED chips.
Let's record this number 6144 too.
3. The formula - "scan mode = total pins amount of LED driving IC / total LED chips amount"
Finally we get the result 384 / 6144 = 1/16