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{{Box|type=l_green_light|text=<br />
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[[Category:8051_tutorials]]
=Objective=
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As per the name the 2x16 has 2 lines with 16 chars on each line. It supports all the ASCII chars and is basically used for displaying the alphanumeric characters. Here each character is displayed in a matrix of 5x7 pixels.
In this tutorial, we will see how we could interface a simple switch to micrcontroller. Yes, it is indeed very simple, later in this tutorial we will do some logical operations with LEDs and Switches.<br />
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Apart from alphanumeric chars it also provides the provision to display the custom characters by creating the pattern.
<br />
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=Switch Basics=
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=LCD UNIT=
[[File:Switch Interface 8051.PNG|150x300px|right|Figure 1: A basic Switch]]
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Let us look at a pin diagram of a commercially available LCD like '''JHD162''' which uses a '''HD44780''' controller and then describe its operation.
If we directly connect a switch to one of the microcontroller port pins, the pin floats when the switch is open. Meaning, it is not at a fixed logic level 0v or 5v. Hence we pull the pin up through a resistor to 5v'''(LOGIC 1)''', as shown in the figure 1. Now, whenever the switch is pressed, it grounds'''(LOGIC 0)''' the port pin.<br />
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[[FILE:Pic16f877aLcdInterface.png]]
<br />
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Now we could go ahead and interface it to the microcontroller, but we would rather interface 8 switches and 8 LED's to two ports as shown in the schematic below.<br />
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{| class="table table-striped table-hover table-condensed table-bordered"
<br />
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|-class="info"
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| Pin Number || Symbol || Pin Function
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|-
 +
|1 || VSS ||Ground
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|-
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| 2|| VCC || +5v
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|-
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| 3 || VEE || Contrast adjustment (VO)
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|-
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| 4 || RS || Register Select. 0:Command, 1: Data
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|-
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| 5 || R/W || Read/Write, R/W=0: Write & R/W=1: Read
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|-
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| 6|| EN || Enable. Falling edge triggered
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|-
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| 7 || D0 || Data Bit 0 (Not used in 4-bit operation)
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|-       
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| 8 || D1 || Data Bit 1 (Not used in 4-bit operation)
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|-       
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| 9 || D2 || Data Bit 2 (Not used in 4-bit operation)
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|-
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| 10 || D3 || Data Bit 3 (Not used in 4-bit operation)
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|-
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| 11 || D4 || Data Bit 4
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|-         
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| 12 || D5 || Data Bit 5
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|-         
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| 13 || D6 || Data Bit 6
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|-         
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| 14 || D7 || Data Bit 7/Busy Flag
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|-
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| 15 || A/LED+ || Back-light Anode(+)
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|-
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| 16 || K/LED- || Back-Light Cathode(-)
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|}
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<br/>
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<br/>
  
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Apart from the voltage supply connections the important pins from the programming perspective are the data lines(8-bit Data bus), Register select, Read/Write and Enable pin.<br><br> 
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<b>Data Bus:</b> As shown in the above figure and table, an alphanumeric LCD has an 8-bit data bus referenced as D0-D7.
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As it is an 8-bit data bus, we can send the data/cmd to LCD in bytes. It also provides the provision to send the data/cmd in chunks of 4-bit, which is used when there are limited number of GPIO lines on the microcontroller.<br><br> 
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<b>Register Select(RS):</b> The LCD has two register namely a Data register and Command register. Any data that needs to be displayed on the LCD has to be written to the data register of LCD. Command can be issued to LCD by writing it to Command register of LCD.
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This signal is used to differentiate the data/cmd received by the LCD.<br>
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If the RS signal is <b>LOW</b> then the LCD interprets the 8-bit info as <b>Command</b> and writes it <b>Command register</b> and performs the action as per the command.<br> 
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If the RS signal is <b>HIGH</b> then the LCD interprets the 8-bit info as <b>data</b> and copies it to <b>data register</b>. After that the LCD decodes the data for generating the 5x7 pattern and finally displays on the LCD.<br><br> 
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<b>Read/Write(RW):</b> This signal is used to write the data/cmd to LCD and reads the  busy flag of LCD.
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For write operation the RW should be <b>LOW</b> and for read operation the R/W should be <b>HIGH</b>.<br><br> 
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<b>Enable(EN):</b> This pin is used to send the enable trigger to LCD.
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After sending the data/cmd, Selecting the data/cmd register, Selecting the Write operation. An HIGH-to-LOW pulse has to be sent on this enable pin which will latch the info into the LCD register and triggers the LCD to act accordingly.
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<br/>
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<br/>
  
 
=Schematic=
 
=Schematic=
[[File:8051 SwitchesLEDs INTERFACE.PNG|650x400px|framed|Figure 2: Schematic Diagram]]
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Below schematic shows the minimum connection required for interfacing the LCD with the microcontroller.<br>
As we can see the schematic has basic circuits for oscillator, reset and power connections for the micrcontroller. <br />
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As we are interfacing the LCD in 4-bit mode, only the higher 4 data lines are used as the data bus.
*A DIP (dual in line package) Switch, array of 8 switches is connected to '''PORT3''' AND 8 LEDs to '''PORT2'''.<br />
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<br><br>
*Observe the '''RR1''' component, it is array of 8 resistors in a single pack(SIP). It is as good as connecting 8 pullup resistors as shown in figure 1. You could also use 8 discrete resistors as well.
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}}
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 +
=Port Connection=
 +
This section shows how to configure the GPIO for interfacing the LCD.<br>
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The below configuration is as per the above schematic. You can connect the LCD to any of the PORT pins available on your boards and update this section accordingly
 +
<html>
 +
<script src="https://gist.github.com/SaheblalBagwan/2c051cee1f15cfd4329a945e2e3fa63e.js"></script>
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</html>
  
=Experiments=
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=LCD Operation=
{{Popup|type=l|text=<br/>
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In this section, we are going to see how to send the data/cmd to the LCD along with the timing diagrams.
======1. Read Switches and Display Status on LEDs======
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First let's see the timing diagram for sending the data and the command signals(RS,RW,EN), accordingly, we write the algorithm and finally the code.
This a very simple one, configure PORT3 (switches) as inputs and PORT2 (LEDs) as outputs; read the switch status and display on LEDs.
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======2. Logical Operations with LEDs and Switches======
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For this experiment, we will divide switches into three groups as shown in table 1. Switches connected to '''P3.7 and P3.6''' are Operators,they are selected as shown in table 2 to perform '''bit-wise''' logical operations on '''Group A''' and '''Group B'''.
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}}
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<syntaxhighlight>
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===Timing Diagram===
1. Read Switches and Display Status on LEDs
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The below image shows the timing diagram for sending the data to the LCD.<br>
#include<reg51.h>
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As shown in the timing diagram  the data is written after sending the RS and RW signals. It is still ok to send the data before these signals.<br>
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The only important thing is the data should be available on the databus before generating the High-to-Low pulse on EN pin.
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[[File:LCD CmdWrite.jpg|figure: command write]]
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<br><br>
  
#define SWITCHES P3
 
#define LEDS  P2
 
  
void main()
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===Steps for Sending Command:===
{
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*step1: Send the I/P command to LCD.
  unsigned char switchInput;
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*step2: Select the Control Register by making RS low.
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*step3: Select Write operation making RW low.
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*step4: Send a High-to-Low pulse on Enable PIN with some delay_us.
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<html>
 +
<script src="https://gist.github.com/SaheblalBagwan/4a521e33274ae73b7b492611ed20d762.js"></script>
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</html>
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<br><br>
  
  SWITCHES = 0xff;            /*Configure SWITCHES as Input */
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===Steps for Sending Data:===
 
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*step1: Send the character to LCD.
  while(1)
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*step2: Select the Data Register by making RS high.
  {
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*step3: Select Write operation making RW low.
      switchInput = SWITCHES;  /* Get the SWITCH combination */
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*step4: Send a High-to-Low pulse on Enable PIN with some delay_us.
      LEDS= switchInput; /* Dispaly the SWITCH I/P on LEDS */
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The timings are similar as above only change is that '''RS''' is made high for selecting Data register.
  }
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}
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</syntaxhighlight>
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 +
<html>
 +
<script src="https://gist.github.com/SaheblalBagwan/19146e69651dc5465bdac99f75c31a29.js"></script>
 +
</html>
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<br><br>
  
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=Hardware Connections=
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[[File:Lcd 4-Bit Tutorial.png]]
  
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= Code Examples =
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Here is the complete code for displaying the data on 2x16 LCD in 4-bit mode.
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<html>
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<script src="https://gist.github.com/SaheblalBagwan/3827aa5155b70f2745ea53ef2dd44574.js"></script>
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</html>
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<br><br>
  
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=Using Explore Embedded Libraries :=
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In the above tutorial, we just discussed how to interface 2x16Lcd in 4-bit mode.<br>
 +
Once you know the working of LCD, you can directly use the ExploreEmbedded libraries to play around with your LCD.<br>
 +
For that you need to include the lcd.c/lcd.h and the associated files(delay/stdutils).<br>
  
'''Table:1'''
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The below sample code shows how to use the already available LCD functions.
{|class ="wikitable" style="text-align:center;margin: 1em auto 1em auto"
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==LCD 1x16==
|-
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<html>
!colspan=2|'''Operation'''||colspan=3|'''Group A'''||colspan=3|'''Group B'''
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<script src="https://gist.github.com/SaheblalBagwan/3329928508b185f1fad661a07f28d6c6.js"></script>
|-
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</html>
|P3.7||P3.6||P3.5||P3.4||P3.3||P3.2||P3.1||P3.0
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|}
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'''Table 2:'''
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{| class ="wikitable" style="text-align:center;margin: 1em auto 1em auto"
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|-
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! '''P3.7''' !! '''P3.6''' !! '''Operation'''
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|-
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| 0||0|| AND
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|-
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| 0||1|| OR
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|-
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| 1||0|| XOR
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|-
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| 1||1|| INVERT(group A)
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|}
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<syntaxhighlight>
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2. Logical Operations with LEDs and Switches
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#include<reg51.h>
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#define SWITCHES P3
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==LCD 2x16==
#define LEDS  P2
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<html>
 +
<script src="https://gist.github.com/SaheblalBagwan/05cb28c2b0ee15b69bd630c498e1bcdb.js"></script>
 +
</html>
  
void main()
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==LCD 4x20==
{
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<html>
  unsigned char operation,groupA,groupB,result;
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<script src="https://gist.github.com/SaheblalBagwan/7c4da4bc35c7ffc5e964e1c31c673497.js"></script>
 +
</html>
  
  SWITCHES = 0xff;                          /*Configure SWITCHES as Input */
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[[FILE:01LCD 4bit.png]]
 
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  while(1)
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  {
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      operation = ((SWITCHES >> 6) & 0x03); /*extract the operation(D6,D7)  */
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      groupA    = ((SWITCHES >> 3) & 0x07); /*extract the groupA I/P(D5-D3) */
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      groupB    =  (SWITCHES & 0x07);        /*extract the groupB I/P(D2-D0) */
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=Downloads=
      switch(operation)                    /*perform operations as per table*/
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Download the sample code and design files from [https://github.com/ExploreEmbedded/8051_DevelopmentBoard this link].
        {
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  case 0x00:  result = groupA & groupB; /* Perform AND operation*/
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              break;
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  case 0x01:  result = groupA | groupB; /* Perform OR operation*/
 
      break;
 
 
 
  case 0x02:  result = groupA ^ groupB; /* Perform XOR operation*/
 
      break;
 
 
 
  case 0x03:  result = (~groupA) & 0x07; /*Invert value of groupA*/
 
      break;
 
 
 
  default: result = 0x00;
 
      break;    
 
        }
 
  
          LEDS= result;       /* Finally dispaly the result on the LEDS */
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Have an opinion, suggestion , question or feedback about the article let it out here!
    }
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{{DISQUS}}
}
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</syntaxhighlight>
+

Latest revision as of 10:15, 2 September 2016

As per the name the 2x16 has 2 lines with 16 chars on each line. It supports all the ASCII chars and is basically used for displaying the alphanumeric characters. Here each character is displayed in a matrix of 5x7 pixels. Apart from alphanumeric chars it also provides the provision to display the custom characters by creating the pattern.


LCD UNIT

Let us look at a pin diagram of a commercially available LCD like JHD162 which uses a HD44780 controller and then describe its operation. Pic16f877aLcdInterface.png

Pin Number Symbol Pin Function
1 VSS Ground
2 VCC +5v
3 VEE Contrast adjustment (VO)
4 RS Register Select. 0:Command, 1: Data
5 R/W Read/Write, R/W=0: Write & R/W=1: Read
6 EN Enable. Falling edge triggered
7 D0 Data Bit 0 (Not used in 4-bit operation)
8 D1 Data Bit 1 (Not used in 4-bit operation)
9 D2 Data Bit 2 (Not used in 4-bit operation)
10 D3 Data Bit 3 (Not used in 4-bit operation)
11 D4 Data Bit 4
12 D5 Data Bit 5
13 D6 Data Bit 6
14 D7 Data Bit 7/Busy Flag
15 A/LED+ Back-light Anode(+)
16 K/LED- Back-Light Cathode(-)



Apart from the voltage supply connections the important pins from the programming perspective are the data lines(8-bit Data bus), Register select, Read/Write and Enable pin.

Data Bus: As shown in the above figure and table, an alphanumeric LCD has an 8-bit data bus referenced as D0-D7. As it is an 8-bit data bus, we can send the data/cmd to LCD in bytes. It also provides the provision to send the data/cmd in chunks of 4-bit, which is used when there are limited number of GPIO lines on the microcontroller.

Register Select(RS): The LCD has two register namely a Data register and Command register. Any data that needs to be displayed on the LCD has to be written to the data register of LCD. Command can be issued to LCD by writing it to Command register of LCD. This signal is used to differentiate the data/cmd received by the LCD.
If the RS signal is LOW then the LCD interprets the 8-bit info as Command and writes it Command register and performs the action as per the command.
If the RS signal is HIGH then the LCD interprets the 8-bit info as data and copies it to data register. After that the LCD decodes the data for generating the 5x7 pattern and finally displays on the LCD.

Read/Write(RW): This signal is used to write the data/cmd to LCD and reads the busy flag of LCD. For write operation the RW should be LOW and for read operation the R/W should be HIGH.

Enable(EN): This pin is used to send the enable trigger to LCD. After sending the data/cmd, Selecting the data/cmd register, Selecting the Write operation. An HIGH-to-LOW pulse has to be sent on this enable pin which will latch the info into the LCD register and triggers the LCD to act accordingly.

Schematic

Below schematic shows the minimum connection required for interfacing the LCD with the microcontroller.
As we are interfacing the LCD in 4-bit mode, only the higher 4 data lines are used as the data bus.

Port Connection

This section shows how to configure the GPIO for interfacing the LCD.
The below configuration is as per the above schematic. You can connect the LCD to any of the PORT pins available on your boards and update this section accordingly

LCD Operation

In this section, we are going to see how to send the data/cmd to the LCD along with the timing diagrams. First let's see the timing diagram for sending the data and the command signals(RS,RW,EN), accordingly, we write the algorithm and finally the code.

Timing Diagram

The below image shows the timing diagram for sending the data to the LCD.
As shown in the timing diagram the data is written after sending the RS and RW signals. It is still ok to send the data before these signals.
The only important thing is the data should be available on the databus before generating the High-to-Low pulse on EN pin. figure: command write


Steps for Sending Command:

  • step1: Send the I/P command to LCD.
  • step2: Select the Control Register by making RS low.
  • step3: Select Write operation making RW low.
  • step4: Send a High-to-Low pulse on Enable PIN with some delay_us.



Steps for Sending Data:

  • step1: Send the character to LCD.
  • step2: Select the Data Register by making RS high.
  • step3: Select Write operation making RW low.
  • step4: Send a High-to-Low pulse on Enable PIN with some delay_us.

The timings are similar as above only change is that RS is made high for selecting Data register.



Hardware Connections

Lcd 4-Bit Tutorial.png

Code Examples

Here is the complete code for displaying the data on 2x16 LCD in 4-bit mode.

Using Explore Embedded Libraries :

In the above tutorial, we just discussed how to interface 2x16Lcd in 4-bit mode.
Once you know the working of LCD, you can directly use the ExploreEmbedded libraries to play around with your LCD.
For that you need to include the lcd.c/lcd.h and the associated files(delay/stdutils).

The below sample code shows how to use the already available LCD functions.

LCD 1x16

LCD 2x16

LCD 4x20

01LCD 4bit.png

Downloads

Download the sample code and design files from this link.


Have an opinion, suggestion , question or feedback about the article let it out here!