Starting from:
$29
Assignment 3_Introduction to peripherals: LCD
Assignment 3
Objectives • Introduction to peripherals: LCD • Practice with C strings and indirect addressing • Exposure to the issues around busy-waiting
AVR Studio Project As in assignment 2, you should create a new assembly language project in AVR Studio for this assignment. Download the sample code and add the files to the project.
The LCD The boards we are using have a Hitachi HD44780 compatible LCD display attached. This LCD display has its own (simple) processor that you must communicate with using a specific protocol in order to initialize and control the LCD screen. You can learn more about how the LCD controller works by looking at the data sheet: https://www.sparkfun.com/datasheets/LCD/HD44780.pdf Luckily for you, a former student has written a library which does all the hard work communicating with the LCD controller and all you have to do is use the subroutines they have written. The table below lists the subroutines, their parameters and what they do. Subroutine Parameters (passed on the stack) Description lcd_init None Initializes the LCD screen. This subroutine must be called before any other subroutine in the LCD library is used. lcd_gotoxy X – 1 byte Y – 1 byte Move the LCD cursor to position (x,y). The first line on the LCD is line 0, the second line is line 1. lcd_puts Address of C-String in data memory – 2 bytes Display the null terminated string at the current cursor position. This routine does no length checking. It is up to you to make sure the string isn't longer than the available space on the LCD. lcd_clr None Clear the LCD screen. str_init Address of source string in Program Memory – 2 bytes Address of destination string in Data Memory – 2 bytes Copy a C string from program memory into data memory.
You've been given a sample program that shows you how to use these LCD functions in the file: lcd_example.asm.
Part I – Simple LCD scrolling You've seen LCD screens in various devices where the message scrolls across the screen. In this assignment you will create your own scrolling message device. In this assignment we will have two messages that are scrolled across the LCD, one message on the first line, and another message on the second line. For discussion purposes, assume that: msg1 = “This is the first message displayed on the first line of the LCD.” msg2 = “On the second line of the LCD there is another message that is scrolled.” When the program first starts, the LCD screen will contain: This is the firs And on the secon
After approximately ½ a second, the LCD screen will be updated to contain:
his is the first nd on the second
And so on, so that approximately every ½ second the message will scroll one character to the left. One important point is what happens when either of the messages near the end. The messages are to be treated as if they wrap-around. For example, at some point, the LCD will contain:
of the LCD.This that is scrolle
Which shows that the first message has wrapped around to the start, while the second hasn't yet reached the end.
Implementation Hints
Data Definitions
WARNING: DO NOT include a .org directive in your data segment. The lcd library has already used the .org directive and if you use it again, you will overwrite internal storage for the lcd library.
Your instructor's solution has the following in the data segment: ; sample strings ; These are in program memory msg1_p: .db "This is the message on the first line. Here it goes.", 0 msg2_p: .db "--- buy --- more --- pop --- buy ", 0
.dseg ; ; The program copies the strings from program memory ; into data memory. ; l1ptr and l2ptr index into these strings ; msg1: .byte 200 msg2: .byte 200
; These strings contain the 16 characters to be displayed on the LCD ; Each time through the loop, the pointers l1ptr and l2ptr are incremented ; and then 16 characters are copied into these memory locations line1: .byte 17 line2: .byte 17
; These keep track of where in the string each line currently is l1ptr: .byte 2 l2ptr: .byte 2
Suggested Code Structure With these data definitions shown above, the main loop of the scrolling application looks like: initialize the lcd clear the lcd copy the strings from program to data memory set l1ptr and l2ptr to point at the start of the display strings do forever: clear line1 and line2 display line1 and line2 copy from the pointers in msg1 and msg2 to line1 and line2 display line1 and line2 move the pointers forward (wrap around when appropriate) delay
You should make extensive use of subroutines in your code. In your instructor's solution, each line above is its own subroutine. Including the delay code (which you can borrow from your lab) your instructor's solution is ~300 lines of assembly language
Objectives • Introduction to peripherals: LCD • Practice with C strings and indirect addressing • Exposure to the issues around busy-waiting
AVR Studio Project As in assignment 2, you should create a new assembly language project in AVR Studio for this assignment. Download the sample code and add the files to the project.
The LCD The boards we are using have a Hitachi HD44780 compatible LCD display attached. This LCD display has its own (simple) processor that you must communicate with using a specific protocol in order to initialize and control the LCD screen. You can learn more about how the LCD controller works by looking at the data sheet: https://www.sparkfun.com/datasheets/LCD/HD44780.pdf Luckily for you, a former student has written a library which does all the hard work communicating with the LCD controller and all you have to do is use the subroutines they have written. The table below lists the subroutines, their parameters and what they do. Subroutine Parameters (passed on the stack) Description lcd_init None Initializes the LCD screen. This subroutine must be called before any other subroutine in the LCD library is used. lcd_gotoxy X – 1 byte Y – 1 byte Move the LCD cursor to position (x,y). The first line on the LCD is line 0, the second line is line 1. lcd_puts Address of C-String in data memory – 2 bytes Display the null terminated string at the current cursor position. This routine does no length checking. It is up to you to make sure the string isn't longer than the available space on the LCD. lcd_clr None Clear the LCD screen. str_init Address of source string in Program Memory – 2 bytes Address of destination string in Data Memory – 2 bytes Copy a C string from program memory into data memory.
You've been given a sample program that shows you how to use these LCD functions in the file: lcd_example.asm.
Part I – Simple LCD scrolling You've seen LCD screens in various devices where the message scrolls across the screen. In this assignment you will create your own scrolling message device. In this assignment we will have two messages that are scrolled across the LCD, one message on the first line, and another message on the second line. For discussion purposes, assume that: msg1 = “This is the first message displayed on the first line of the LCD.” msg2 = “On the second line of the LCD there is another message that is scrolled.” When the program first starts, the LCD screen will contain: This is the firs And on the secon
After approximately ½ a second, the LCD screen will be updated to contain:
his is the first nd on the second
And so on, so that approximately every ½ second the message will scroll one character to the left. One important point is what happens when either of the messages near the end. The messages are to be treated as if they wrap-around. For example, at some point, the LCD will contain:
of the LCD.This that is scrolle
Which shows that the first message has wrapped around to the start, while the second hasn't yet reached the end.
Implementation Hints
Data Definitions
WARNING: DO NOT include a .org directive in your data segment. The lcd library has already used the .org directive and if you use it again, you will overwrite internal storage for the lcd library.
Your instructor's solution has the following in the data segment: ; sample strings ; These are in program memory msg1_p: .db "This is the message on the first line. Here it goes.", 0 msg2_p: .db "--- buy --- more --- pop --- buy ", 0
.dseg ; ; The program copies the strings from program memory ; into data memory. ; l1ptr and l2ptr index into these strings ; msg1: .byte 200 msg2: .byte 200
; These strings contain the 16 characters to be displayed on the LCD ; Each time through the loop, the pointers l1ptr and l2ptr are incremented ; and then 16 characters are copied into these memory locations line1: .byte 17 line2: .byte 17
; These keep track of where in the string each line currently is l1ptr: .byte 2 l2ptr: .byte 2
Suggested Code Structure With these data definitions shown above, the main loop of the scrolling application looks like: initialize the lcd clear the lcd copy the strings from program to data memory set l1ptr and l2ptr to point at the start of the display strings do forever: clear line1 and line2 display line1 and line2 copy from the pointers in msg1 and msg2 to line1 and line2 display line1 and line2 move the pointers forward (wrap around when appropriate) delay
You should make extensive use of subroutines in your code. In your instructor's solution, each line above is its own subroutine. Including the delay code (which you can borrow from your lab) your instructor's solution is ~300 lines of assembly language
1 file (90.9KB)
