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Altera_Forum
Honored Contributor I
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2-Line Display & Custom Character Creation and Display

I apologize in advance as I am very new to all of this so my vocabulary will probably be very layman. I will try to provide as much information as possible. 

 

I am currently working with a Nios II processor DE0 board. 

A snapshot of the LCD I am working with is 

https://www.alteraforum.com/forum/attachment.php?attachmentid=7834 The number after that is ST7066U 

 

I am trying to write in assembly language a program that will allow me to use 2 lines on the display. 

 

I also want to create a custom character to display. After reading the instruction manual, I learned about writing to DDRAM and GCRAM, but I have no idea how. 

 

Any help would be appreciated. 

 

Below is what I have figured out how to write to display: 

 

 

 

 

 

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Altera_Forum
Honored Contributor I
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.global alt_main 

 

 

.text 

alt_main: 

movia sp, 0x00800000 //Set up stack address 

movia r10, 0x10000040 //Assigns r10 to address for slider switch 

movi r9, 0b00 //Used as initial contents of slider switch 

movi r11, 0b001 //Assigns value for SW0 

movi r12, 0b010 //Assigns value for SW1 

movi r13, 0b011 //Assigns value for SW2 

movia r17, 0x00800030 //Assigns r17 to address for LCD control port 

movia r16, 0x00800040 //Assigns r18 to address for LCD data port 

call LCDportInit //Sets the port for the LCD to OUTPUT 

call LCDinit //Sets the details that the LCD will follow 

 

 

 

 

slider_check: 

ldbio r9, 0(r10) //Loads contents of the slider switch 

andi r9, r9, 0b011 //Checks only first 3 bits/switches 

beq r9, r0, slider_check //Loop if 0 

beq r4, r9, slider_check //Loop is same as the check register r4 

mov r4, r9 //Store new check register as equivalent to r9 

beq r9, r11, Hello //If only first slider is on, branch to Hello 

beq r9, r12, HowAreYou //If only second slider is on, branch to HowAreYou 

beq r9, r13, IAmFine //If only third slider is on, branch to IAmFine 

 

 

 

 

Hello: 

movia r18, Message1 //Assigns r18 as the address of Message1 

call LCDprintString //Run the subroutine to print the message 

br slider_check 

 

 

HowAreYou: 

movia r18, Message2 //Assigns r18 as the address of Message2 

call LCDprintString //Run the subroutine to print the message 

br slider_check 

 

 

 

IAmFine: 

movia r18, Message3 //Assigns r18 as the address of Message3 

call LCDprintString //Run the subroutine to print the message 

br slider_check 

 

 

 

LCDcmdWrt: 

subi sp, sp, 8 //Make room on stack 

stw r6, 0(sp) //Save r6 

stw ra, 4(sp) //Save ra incase another 

//subroutine is called 

call delay_20ms //Time needed to perform command 

movi r6, 0 //E=RS=RW=0 

stbio r6, 0(r17) //LCD control port 

stbio r7, 0(r16) //Send command to LCD data port. The command 

//is passed to subroutine in r7 

ori r6, r6, 0b100 //E = 1 

stbio r6, 0(r17) //LCD control port 

call delay_500ns //Keep E high > 450ns 

andi r6, r6, 0b11111011 //E = 0 

stbio r6, 0(r17) //LCD control port 

 

 

ldw r6, 0(sp) //restore r6 

ldw ra, 4(sp) //restore ra 

addi sp, sp, 8 //restore sp up to initial address 

ret 

 

 

 

LCDdataWrt: 

subi sp, sp, 8 //Make room on stack 

stw r6, 0(sp) //Save r6 

stw ra, 4(sp) //Save ra incase another subroutine is called 

 

 

call delay_20ms //Time needed to perform command 

movi r6, 0b010 //E=0 RS=1 RW=0 

stbio r6, 0(r17) //LCD control port 

stbio r7, 0(r16) //Send command to LCD data port. The command 

//is passed to subroutine in r7 

ori r6, r6, 0b100 //E = 1 

stbio r6, 0(r17) //LCD control port 

call delay_500ns //Keep E high > 450ns 

andi r6, r6, 0b11111011 //E = 0 

stbio r6, 0(r17) //LCD control port 

 

 

ldw r6, 0(sp) //restore r6 

ldw ra, 4(sp) //restore ra 

addi sp, sp, 8 //restore sp up to initial address 

ret 

 

 

 

LCDportInit: 

subi sp, sp, 8 //Make room on stack 

stw r6, 0(sp) //Save r6 

stw ra, 4(sp) //Save ra incase another subroutine is called 

 

 

movi r6, 0xff //Value used to initiate the LCD as OUTPUT 

stbio r6, 4(r17) //Store to LCD control port 

stbio r6, 4(r16) //Store to LCD data port 

 

 

ldw r6, 0(sp) //restore r6 

ldw ra, 4(sp) //restore ra 

addi sp, sp, 8 //restore sp up to initial address 

ret 

 

 

 

LCDinit: 

subi sp, sp, 4 //Make room on stack 

stw ra, 0(sp) //Save ra 

 

 

movi r7, 0x38 //Data length 8-bits, 5x7 font 

call LCDcmdWrt 

movi r7, 0x0f //display ON, cursor ON, cursor Blink 

call LCDcmdWrt 

movi r7, 0x01 //clear display 

call LCDcmdWrt 

movi r7, 0x06 //increment cursor position 

call LCDcmdWrt 

movi r7, 0x02 //home cursor 

call LCDcmdWrt 

 

 

ldw ra, 0(sp) //restore ra 

addi sp, sp, 4 //restore sp up to initial address 

ret 

 

 

 

LCDprintString: 

subi sp, sp, 8 //Make room on stack 

stw r7, 0(sp) //Save r7 

stw ra, 4(sp) //Save ra 

 

 

movi r7, 0x01 //clear display 

call LCDcmdWrt 

movi r7, 0x02 //home cursor 

call LCDcmdWrt 

 

 

next_char: 

ldb r7, 0(r18) //Load the current character in the string 

beq r7, r0, end_printString //If LCD has reached the '0' at the end 

//of the string, go to end_printString 

call LCDdataWrt //Run the subroutine LCDdataWrt 

addi r18, r18, 0x01 //Add 1 to the character string value 

br next_char //Loop the current subroutine 

 

 

end_printString: 

ldw r7, 0(sp) //Restore r7 

ldw ra, 4(sp) //Restore ra 

addi sp, sp, 8 //Restore sp up to initial address 

ret 

 

 

 

delay_20ms: 

subi sp, sp, 8 //Allocate 8 bytes on stack 

stw r6, 0(sp) //Save r6 

stw ra, 4(sp) //Save return address, allows nesting subroutines 

movia r6, 45455 //This value allows for 20ms to pass 

again_20ms: 

subi r6, r6, 1 

bne r6, r0, again_20ms 

ldw r6, 0(sp) //Restore r6 

ldw ra, 4(sp) //Restore return address 

addi sp, sp, 8 //de-allocate stack locations 

ret 

 

 

 

delay_500ns: 

andi r0, r0, 0b0 //These instructions will provide enough 

andi r0, r0, 0b0 //time to complete the necessary delay time 

ret 

 

 

 

.data 

 

Message1: 

.asciz "Hello" 

 

 

Message2: 

.asciz "How are you?" 

 

 

Message3: 

.asciz "I am fine" 

 

 

.end
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