Sending Commands to LCD

To send commands we simply need to select the command register. Everything is same as we have done in the initialization routine. But we will summarize the common steps and put them in a single subroutine. Following are the steps:
  • Move data to LCD port
  • select command register
  • select write operation
  • send enable signal
  • wait for LCD to process the command

Keeping these steps in mind we can write LCD command routine as.


;Ports used are same as the previous example
;Routine to send command to LCD

LCD_command:
         mov   LCD_data,A     ;Move the command to LCD port
         clr   LCD_rs         ;Selected command register
         clr   LCD_rw         ;We are writing in instruction register
         setb  LCD_en         ;Enable H->
L
         clr   LCD_en
         acall LCD_busy       ;Wait for LCD to process the command
         ret                  ;Return from busy routine

; Usage of the above routine
; A will carry the command for LCD
; e.g. we want to send clear LCD command
;
; mov   a,#01H         ;01H is command for clearing LCD
; acall LCD_command    ;Send the command

The equivalent C code Keil C compiler. Similar code can be written for SDCC.

void LCD_command(unsigned char var)
{
     LCD_data = var;      //Function set: 2 Line, 8-bit, 5x7 dots
     LCD_rs   = 0;        //Selected command register
     LCD_rw   = 0;        //We are writing in instruction register
     LCD_en   = 1;        //Enable H->
L
     LCD_en   = 0;
     LCD_busy();          //Wait for LCD to process the command
}
// Using the above function is really simple
// var will carry the command for LCD
// e.g.
//
// LCD_command(0x01);

Setting cursor position on LCD
To set the cursor position on LCD, we need to send the DDRAM address...
Bit7  6   5   4   3   2   1   0
 1   AD6 AD5 AD4 AD3 AD2 AD1 AD0

The seventh bit is always 1, and bit 0 to 7 are DDRAM address (See the introduction section of LCD). so if you want to put the cursor on first position the address will be '0b0000000' in binary and 7th bit is 1. so address will be 0x80, so for DDRAM all address starts from 0x80.

For 2 line and 16 character LCD. The address from 0x80 to 0x8F are visible on first line and 0xC0 to 0xCF is visible on second line, rest of the DDRAM area is still available but is not visible on the LCD, if you want to check this thing, then simply put a long sting greater than 16 character and shift the entire display, you will see all the missing character coming from the back.. this way you can make scrolling line on LCD (see more on shifting display in commands section).

Below is an example for setting cursor position on LCD.

;We are placing the cursor on the 4th position
;so the DDRAM address will be 0x03
;and the command will be 0x80+0x03 = 0x83
mov a,#83H           ;load the command
acall LCD_command    ;send command to LCD
// to do the same thing is C
// as we done before
LCD_command(0x83);

Sending Data to LCD

To send data we simply need to select the data register. Everything is same as the command routine. Following are the steps:
  • Move data to LCD port
  • select data register
  • select write operation
  • send enable signal
  • wait for LCD to process the data

Keeping these steps in mind we can write LCD command routine as.


;Ports used are same as the previous example
;Routine to send data (single character) to LCD

LCD_senddata:
         mov   LCD_data,A     ;Move the command to LCD port
         setb  LCD_rs         ;Selected data register
         clr   LCD_rw         ;We are writing
         setb  LCD_en         ;Enable H->
L
         clr   LCD_en
         acall LCD_busy       ;Wait for LCD to process the data
         ret                  ;Return from busy routine

; Usage of the above routine

; A will carry the character to display on LCD
; e.g. we want to print A on LCD
;
; mov   a,#'A'         ;Ascii value of 'A' will be loaded in accumulator

; acall LCD_senddata   ;Send data

The equivalent C code Keil C compiler. Similar code can be written for SDCC.

void LCD_senddata(unsigned char var)
{
     LCD_data = var;      //Function set: 2 Line, 8-bit, 5x7 dots
     LCD_rs   = 1;        //Selected data register
     LCD_rw   = 0;        //We are writing
     LCD_en   = 1;        //Enable H->
L
     LCD_en   = 0;
     LCD_busy();          //Wait for LCD to process the command
}
// Using the above function is really simple
// we will pass the character to display as argument to function
// e.g.
//
// LCD_senddata('A');

Now you have seen that its really easy to send command and data to LCD. Now what if we have a string to send to LCD? how we are going to do that?

Is simple, we will store the LCD string in the ROM of controller and call the string character by character. A simple exmple is shown below.


;Sending string to LCD Example

LCD_sendstring:
         clr   a                 ;clear Accumulator for any previous data
         movc  a,@a+dptr         ;load the first character in accumulator
         jz    exit              ;go to exit if zero
         acall lcd_senddata      ;send first char
         inc   dptr              ;increment data pointer
         sjmp  LCD_sendstring    ;jump back to send the next character
exit:
         ret                     ;End of routine

; Usage of the above routine
; DPTR(data pointer) will carry the address
; of string to send to LCD.
; e.g. we want to print "LCD Tutorial" on LCD then
;

; mov   dptr,#my_string   ;my_string is the label where the string is stored

; acall LCD_sendstring    ;Send string

;

; To store a string..

; my_string:

; DB   "LCD Tutorial", 00H

; 00H indicate that string is finished.

The equivalent C code Keil C compiler. Similar code can be written for SDCC.

void LCD_sendstring(unsigned char *var)
{
     while(*var)              //till string ends
       LCD_senddata(*var++);  //send characters one by one
}
// Using the above function is really simple
// we will pass the string directly to the function
// e.g.
//
// LCD_sendstring("LCD Tutorial");

Now we are ready with sending data and sending command to LCD. Now the last and final section which is creating custom characters or patterns to display on LCD.

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Fri Feb 05 2016, 08:33 AM
SANJYOT JADHAV
sir did we have to use Gsm modem for testing the circuit on proteus
Tue Feb 02 2016, 11:17 AM
upendra kumar
i want information about 3-phase motor control using gsm technology
Sat Jan 16 2016, 05:33 PM
Kenneth Etuk
Hi everyone, I need help with a project involving MCU,rttc, and DC motor. I will pay for it. please reply to my mail [email protected] if you are interested. thanks
ExperimenterUK
Sat Jan 16 2016, 02:08 AM
@Kabona Log in and create a thread. Tell us what you want to do
Tue Jan 12 2016, 08:24 PM
Kabona
how can I make my pc be input and output device for the microcontroller
Sat Jan 09 2016, 07:04 AM
Ravz
Thank u..... one more doubt Will ultrasonic sensor HC-SR04 works with aurdino board in operating system linux
Tommy.Kofisterix
Fri Jan 08 2016, 08:50 PM
I know it detects also the mud on rear bumper, this means other obstacles will
Tommy.Kofisterix
Fri Jan 08 2016, 08:48 PM
Hey hi, hello
Tue Jan 05 2016, 03:03 PM
Ravz
Anybody here????
Tue Jan 05 2016, 02:52 PM
Ravz
Will ultrasonic sensors detect obstacles when cloth or any other objects covers the sensor????

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designAAA
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ExperimenterUK Avatar
Posted By ExperimenterUK
Thu Feb 04 2016, 04:10 AM
Sir I didn't understand that. Could you explain ab...
sankalp_s Avatar
Posted By sankalp_s
Tue Feb 02 2016, 07:26 PM
but good use of sub routines will save a lot of ...
ExperimenterUK Avatar
Posted By ExperimenterUK
Tue Feb 02 2016, 12:25 AM
after removing ALLON instruction it's working fine...
ExperimenterUK Avatar
Posted By ExperimenterUK
Tue Feb 02 2016, 12:14 AM
Which micro controller are you using ?.Does it hav...
sankalp_s Avatar
Posted By sankalp_s
Sat Jan 30 2016, 07:40 PM
You need to explain exactly what you want the code...
ExperimenterUK Avatar
Posted By ExperimenterUK
Sat Jan 30 2016, 06:57 PM
>sir can you code this in any other method?You nee...
sankalp_s Avatar
Posted By sankalp_s
Sat Jan 30 2016, 06:47 PM
CALL ALLONCLR L1CLR L2CLR L3CLR L4CALL DELAY ;del...
designAAA Avatar
Posted By designAAA
Sat Jan 30 2016, 10:03 AM
I have used to timer 2 external pin for other purp...
designAAA Avatar
Posted By designAAA
Sat Jan 30 2016, 09:00 AM
Hello,I am building the dotmatrix display, where I...
ExperimenterUK Avatar
Posted By ExperimenterUK
Sat Jan 30 2016, 12:40 AM
ok sir but what is solution for it. will i have to...