LCD can be used to display numbers, characters and graphics. Generally the following LCD pins are used to interface with 8051.
D0 – D7 (Data): The 8-bit data pins, DO – D7, are used to send information to the LCD or read the contents of the LCD’s internal registers.
RS (Register Select): There are two very important registers inside the LCD. The RS pin is used for their selection as follows. If RS = 0, the instruction command code register is selected, allowing the user to send a command such as clear display, cursor at home, etc. If RS = 1 the data register is selected, allowing the user to send data to be displayed on the LCD.
R/W (Read Write): R/W input allows the user to write information to the LCD or read information from it. R/W = 1 when reading; R/W = 0 when writing.
E (Enable): The enable pin is used by the LCD to latch information presented to its data pins. When data is supplied to data pins, a high-to-low pulse must be applied to this pin in order for the LCD to latch in the data present at the data pins.
Busy Flag: The busy flag is D7 and can be read when R/W = 1 and RS = 0, as follows: if R/W= 1, RS = 0. When D7 = 1 (busy flag = 1), the LCD is busy taking care of internal operations and will not accept any new information. When D7 = 0, the LCD is ready to receive new information.
To display letters and numbers, we send ASCII codes for the letters A – Z, a – z, and numbers 0 – 9 to data pins while making RS = 1.There are also instruction command codes that can be sent to the LCD. The command codes are in Hex.
Sending commands and data to LCD:
To send any of the commands to the LCD, make pin RS = 0. For data, make RS = 1. Then send a high-to-low pulse to the E pin to enable the internal latch of the LCD. Sending command and data using delay function.
Sending command and data using busy flag and delay:
Send string to LCD:
D0 – D7 (Data): The 8-bit data pins, DO – D7, are used to send information to the LCD or read the contents of the LCD’s internal registers.
RS (Register Select): There are two very important registers inside the LCD. The RS pin is used for their selection as follows. If RS = 0, the instruction command code register is selected, allowing the user to send a command such as clear display, cursor at home, etc. If RS = 1 the data register is selected, allowing the user to send data to be displayed on the LCD.
R/W (Read Write): R/W input allows the user to write information to the LCD or read information from it. R/W = 1 when reading; R/W = 0 when writing.
E (Enable): The enable pin is used by the LCD to latch information presented to its data pins. When data is supplied to data pins, a high-to-low pulse must be applied to this pin in order for the LCD to latch in the data present at the data pins.
Busy Flag: The busy flag is D7 and can be read when R/W = 1 and RS = 0, as follows: if R/W= 1, RS = 0. When D7 = 1 (busy flag = 1), the LCD is busy taking care of internal operations and will not accept any new information. When D7 = 0, the LCD is ready to receive new information.
To display letters and numbers, we send ASCII codes for the letters A – Z, a – z, and numbers 0 – 9 to data pins while making RS = 1.There are also instruction command codes that can be sent to the LCD. The command codes are in Hex.
Sending commands and data to LCD:
To send any of the commands to the LCD, make pin RS = 0. For data, make RS = 1. Then send a high-to-low pulse to the E pin to enable the internal latch of the LCD. Sending command and data using delay function.
ORG 0H MOV A, #38H ; initialize LCD command. 2 lines, 5x7 dot matrix display ACALL COMMWR ; call command write subroutine ACALL DELAY ; give LCD some time MOV A, #0EH ; display on, cursor on command ACALL COMMWR ; call command write subroutine ACALL DELAY ; give LCD some time MOV A, #01H ; clear LCD command ACALL COMMWR ; call command write subroutine ACALL DELAY ; give LCD some time MOV A, #06H ; shift cursor right command ACALL COMMWR ; call command write subroutine ACALL DELAY ; give LCD some time MOV A, #84H ; cursor at line 1 position 4 ACALL COMMWR ; call command write subroutine ACALL DELAY ; give LCD some time MOV A, #'N' ; display letter N ACALL DATAWR ; call data write subroutine ACALL DELAY ; give LCD some time MOV A, #'O' ; display letter O ACALL DATAWR ; call data write subroutine ACALL DELAY ; give LCD some time AGAIN : SJMP AGAIN ; stay here ; send command to LCD COMMWR: MOV P1, A ; copy reg A to port 1 CLR P2.0 ; RS = 0 for command CLR P2.1 ; R/W = 0 for write SETB P2.2 ; E = 1 for high pulse ACALL DELAY ; give LCD some time CLR P2.2 ; E = 0 for high to low pulse RET ; send data to LCD DATAWR: MOV P1, A ; copy reg A to port 1 SETB P2.0 ; RS = 1 for data CLR P2.1 ; R/W = 0 for write SETB P2.2 ; E = 1 for high pulse ACALL DELAY ; give LCD some time CLR P2.2 ; E = 0 for high to low pulse RET ; some delay DELAY: MOV R3, #50 HERE2: MOV R4, #255 HERE: DJNZ R4, HERE ; stay until R4 = 0 DJNZ R3, HERE2 ; stay until R3 = 0v RET END
Sending command and data using busy flag and delay:
ORG 0H MOV A, #38H ; initialize LCD command. 2 lines, 5x7 dot matrix display ACALL COMMWR ; call command write subroutine MOV A, #0EH ; display on, cursor on command ACALL COMMWR ; call command write subroutine MOV A, #01H ; clear LCD command ACALL COMMWR ; call command write subroutine MOV A, #06H ; shift cursor right command ACALL COMMWR ; call command write subroutine MOV A, #84H ; cursor at line 1 position 4 ACALL COMMWR ; call command write subroutine MOV A, #'N' ; display letter N ACALL DATAWR ; call data write subroutine MOV A, #'O' ; display letter O ACALL DATAWR ; call data write subroutine AGAIN : SJMP AGAIN ; stay here ; send command to LCD COMMWR: ACALL READY ; is LCD ready to receive command? MOV P1, A ; copy reg A to port 1 CLR P2.0 ; RS = 0 for command CLR P2.1 ; R/W = 0 for write SETB P2.2 ; E = 1 for high pulse ACALL DELAY ; give LCD some time CLR P2.2 ; E = 0 for high to low pulse RET ; send data to LCD DATAWR: ACALL READY ; is LCD ready to receive data? MOV P1, A ; copy reg A to port 1 SETB P2.0 ; RS = 1 for data CLR P2.1 ; R/W = 0 for write SETB P2.2 ; E = 1 for high pulse ACALL DELAY ; give LCD some time CLR P2.2 ; E = 0 for high to low pulse RET ;read command register and check busy flag READY: SETB P1.7 ; make p1.7 input port CLR P2.0 ; RS = 0 access command register SETB P2.1 ; R/W = 1 read command register BACK: CLR P2.2 ; E = 0 for high to low pulse ACALL DELAY ; give LCD some time SETB P2.2 ; E = 1 for high pulse JB P1.7, BACK ; stay until busy flag = 0 RET ; some delay DELAY: MOV R3, #50 HERE2: MOV R4, #255 HERE: DJNZ R4, HERE ; stay until R4 = 0 DJNZ R3, HERE2 ; stay until R3 = 0v RET END
Send string to LCD:
ORG 0H MOV DPTR, #MYCMD LOOP1: CLR A MOVC A, @A+DPTR ACALL COMMWR ACALL DELAY JZ SEND_DATA INC DPTR SJMP LOOP1 SEND_DATA: MOV DPTR, #MYDATA LOOP2: CLR A MOVC A, @A+DPTR ACALL DATAWR ACALL DELAY JZ SEND_DATA INC DPTR JZ AGAIN SJMP LOOP2 AGAIN : SJMP AGAIN ; stay here ; send command to LCD COMMWR: MOV P1, A ; copy reg A to port 1 CLR P2.0 ; RS = 0 for command CLR P2.1 ; R/W = 0 for write SETB P2.2 ; E = 1 for high pulse ACALL DELAY ; give LCD some time CLR P2.2 ; E = 0 for high to low pulse RET ; send data to LCD DATAWR: MOV P1, A ; copy reg A to port 1 SETB P2.0 ; RS = 1 for data CLR P2.1 ; R/W = 0 for write SETB P2.2 ; E = 1 for high pulse ACALL DELAY ; give LCD some time CLR P2.2 ; E = 0 for high to low pulse RET ; some delay DELAY: MOV R3, #50 HERE2: MOV R4, #255 HERE: DJNZ R4, HERE ; stay until R4 = 0 DJNZ R3, HERE2 ; stay until R3 = 0v RET
ORG 300H MYCMD: DB 38H, 0EH, 01, 06, 84H, 0 MYDATA: DB "HELLO0" END
Related topics:
8051 External Program Memory Interfacing | 8051 External Data Memory Interfacing | 8051 Memory Mapped IO | 8051 LED Interfacing | 8051 Switch Interfacing | 8051 Keyboard Interfacing | 8051 7-Segment Display Interfacing | 8051 ADC Interfacing | 8051 DAC Interfacing | 8051 Relay Interfacing | 8051 Sensor Interfacing | 8051 Stepper Motor Interfacing | 8051 DC Motor Interfacing
List of topics: 8051
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