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I want to simulate **the Entry set mode ** function of and LCD based on HITACHI 44780 Controller. (Here is the datasheet.)

The "Entry set mode" is given the following code of the 8 bits data bus "0 0 0 0 0 1 I/D S" The datasheet says: I/D=0 Decrements the DDRAM address by 1 when a code is written or read I/D=1 Increments the DDRAM address by 1 when a code is written or read S=1 Shifts the entire display either to the right (I/D=0) or to the left (I/D=1) In summary: this function sets the LCD to write from left to right or from right to left and the codes to simulate are (0x04, 0x05, 0x06 and 0x07, these are the combinations of Entry set mode code.)

Here is my AVR assembly program use to simulate these codes (combinations)

; VARIABLES ;==================================================================== .EQU RS=0 .EQU RW=1 .EQU EN=2 .EQU _5us=254 .EQU _100us=155 .EQU _5ms=215 ;Init_Stack pointer LDI R16,HIGH(RAMEND) OUT SPH,R16 LDI R16,LOW(RAMEND) OUT SPL,R16 ;Configure PORTS LDI R16,0xFF OUT DDRA,R16 ;Config PORTA as output OUT DDRB,R16 ;Config PORTB as output LDI R18,0x00 OUT PORTB,R18 ;POWER ON THE LCD LDI R20,_5ms RCALL DELAY RCALL LCD_init RCALL DELAY ;================================================================================================ ;Set the Entry mode LDI R16,0x05 ;Right shift display (Decrement the cursor and enable shift) RCALL CMD_WRT ;================================================================================================ ;Display my message with a shift to right ;I set the cursor at the 7th address of the display range of LCD (0x07) ;and I expect the display to be written in the revers order " OLLEH " ;with a shift to the right starting form 0x07 of LCD ;Display First message starting from 7 position of 1st line LDI R16,0x87 ;Set the cursor at the 7 address (0x07) of the LCD display RCALL CMD_WRT LDI ZH,HIGH(MSG1<<1) LDI ZL,LOW(MSG1<<1) RCALL MS_DISP HERE: RJMP HERE ;==================================================================== LCD_init: PUSH R16 PUSH R20 LDI R20,_5ms LDI R16,0x33 ;Start initialization RCALL CMD_WRT RCALL DELAY LDI R16,0x32 ;Initialization process RCALL CMD_WRT RCALL DELAY LDI R16,0x28 ;Function set to 4bit mode with 2 lines and 5x8 dots RCALL CMD_WRT RCALL DELAY LDI R16,0x0F;..... ;Display ON, Cursor ON,Blinking ON, change the value of R16 for test RCALL CMD_WRT RCALL DELAY LDI R16,0x01 ;Clear Display RCALL CMD_WRT RCALL DELAY LDI R16,0x06;..... ;Set Entry Mode to shift left RCALL CMD_WRT RCALL DELAY POP R20 POP R16 RET CMD_WRT: PUSH R27 PUSH R20 ;High nibble manipulation MOV R27,R16 ANDI R27,0xF0 ;Mask the low nibble and keep the high one OUT PORTA,R27 CBI PORTB,RS ;Set RS=0 for commands SBI PORTB,EN ;Set EN=1 to generate a pulse LDI R20,_5us RCALL DELAY ;Delays the pulse (duration) CBI PORTB,EN ;Reset EN=0 to latch the data LDI R20,_100us ; RCALL DELAY ;Low nibble manipulation MOV R27,R16 SWAP R27 ;Swap the content of R16 to get the low nibbles ANDI R27,0xF0 ;Mask the low nibble and keep the high one OUT PORTA,R27 CBI PORTB,RS ;Set RS=0 for command write SBI PORTB,EN ;Set EN=1 LDI R20,_5us RCALL DELAY CBI PORTB,EN LDI R20,_100us RCALL DELAY POP R20 POP R27 RET DATA_WRT: PUSH R27 PUSH R20 MOV R27,R16 ;Load R27 with the content of R16 ANDI R27,0xF0 ;Mask low nibble and keep high nibble OUT PORTA,R27 SBI PORTB,RS ;Set RS=1 for data write SBI PORTB,EN ;Set EN=1 to allow data latch LDI R20,_5us RCALL DELAY ;Duration of the pulse CBI PORTB,EN LDI R20,_100us RCALL DELAY ;Low nibble manipulation MOV R27,R16 SWAP R27 ;Swap the content of R27 ANDI R27,0xF0 ;Mask the low nibble and keep the high one OUT PORTA,R27 ;Send data to the output port SBI PORTB,RS ;Set RS=1 for data sent SBI PORTB,EN ;Set EN=1 for data latch RCALL DELAY CBI PORTB,EN LDI R20,_100us RCALL DELAY POP R20 POP R27 RET MS_DISP: PUSH R16 PUSH R20 LDI R20,_5ms _DISP:LPM R16,Z+ RCALL DATA_WRT RCALL BIG_DELAY CPI R16,0 BRNE _DISP POP R20 POP R16 RET DELAY: PUSH R17 OUT TCNT0,R20 ;Load TCNT0 with the appropriate prescale LDI R17,0x01 CPI R20,_100us BRNE L1 LDI R17,0x02 L1:CPI R20,_5ms BRNE L2 LDI R17,0x05 L2:OUT TCCR0,R17 ;Normal mode,Int Clk,Prescal=8 for us delay and 1024 for ms delay AGAIN:IN R17,TIFR SBRS R17,TOV0 RJMP AGAIN LDI R17,0x00 OUT TCCR0,R17 ;Turn OFF the timer0 LDI R17,1<<TOV0 OUT TIFR,R17 POP R17 RET BIG_DELAY: PUSH R21 PUSH R20 LDI R20,_5ms LDI R21,0x55 S_DELAY:RCALL DELAY DEC R21 BRNE S_DELAY POP R20 POP R21 RET .ORG 0x200 MSG1: .DB "HELLO ",0

When I simulate my program with the following codes of Entry set mode:

  • 0x04, the message is displayed from right to left starting from the desired DDRAM address (works as expected)
  • 0x06, the message is displayed from left to right starting from de desired LCD position (Works as expected)
  • 0x07, the message is displayed form left to right with a shift starting from de desired LCD position (Works as expected)

But when I provide 0x05 code as in my program, I expect the display to start from position 7 and shift to the right, and the final display should be " OLLEH", but it does not work as it is expected and nothing is displayed (the LCD is like if it is cleared).

Could anyone please explain to me this fact? and what did I miss ?

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  • \$\begingroup\$ So are you running this on a simulator or on real display? What does the AVR code have to do with it, as it might be easier to see what commands and data bytes you send to the display. Also which size display you have? And how the rows and columns are mapped to the display? For example, many 1x16 displays are from the HD44780 point of view 2x8 displays and thus if you don't initialize the display to two lines you get only 1x8 display. \$\endgroup\$ Commented Jul 6, 2024 at 12:47
  • \$\begingroup\$ I run it in simulator "proteus 8", the LCD is 2x16 type and initialised to 4 bits interface mode \$\endgroup\$ Commented Jul 6, 2024 at 12:51
  • \$\begingroup\$ Then you can simply try it without AVR and just use pushbuttons in 8-bit mode to test how the LCD simulation works. Simulators are not always 100% correct. \$\endgroup\$ Commented Jul 6, 2024 at 12:56

1 Answer 1

Reset to default
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I used an online HD44780 display emulator website and did the following:

  • cmd 0x0F to turn display and blinking cursor on

  • cmd 0x87 to go to address 7

  • cmd 0x05 to set decreasing addresses with display shift

  • sent the letters "HELLO"

and the result was that the website showed the following:

  • 7 empty char cells, blinking cursor on 8th char cell, and text "OLLEH", and three empty char cells.

If Proteus failed to emulate this then it did. If all your four cases what you send to display are identical except for the entry mode set command, then the bug cannot be in your AVR code or connections.

Please be aware that emulators may not work exactly like real world chips do. I did not check your code but emulators may ignore things that you have to take into account with real chips, such as how fast you can send data or how long the display is busy executing a command.

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