Lab 3 Handout - Oregon State University
Contents
1. ldi mpr 138 mpr lt 138 ldi XL low 0112 X lt 0112 ldi XH high 0112 X lt 0112 reall Bin2ASCII Call Bin2ASCII There are many other functions within the LCD driver but they are support functions for those described above and should not be called individually Modifying any function within the driver is not recommended as it could damage the performance of the function but feel free to play around if you like With that said if you do modify the driver or add another function that improves the performance let your TA know what you did and how it works or why it is better and we might add it to future versions of the driver Data Manipulation 2014 Oregon State University ECE375 Manual Page 26 Section Three Data Manipulation and the LCD Display To be able to move data from one memory to another you first must understand the memory The ATmega128 is an 8 bit AVR architecture Thus all register and data memory are 8 bit wide and all data is moved around 1 byte at a time However the AVR Op Code is 16 or 32 bits and for efficiency reasons the program memory is 16 bits or 2 bytes wide This means that when you read from the program memory you will have to read 2 bytes for every address space in the program memory When writing a program it is often necessary to include data directly into program memory instead of entering it into the data memory each a time a simulation is run The DB Data By2. Other things that are initialized within the INIT function are ports timers interrupts and other peripherals For this lab you will need to initialize the LCD display To initialize the LCD display you will perform a function call to the LCD Initialization Subroutine You will also need to move data from the program memory to data memory in the INIT function LCD Driver User Manual To successfully use the LCD display for this lab you will need to properly setup and call the functions in the LCD driver To do this you must first include it into your program Unlike the definition file the LCD driver contains actual assembly code and thus cannot be included at the beginning of the program file like the definition file A quick look at the AVR Starters Guide under proper coding structure tells us that any include code file is included at the end of the program i e the last lines The actual LCD driver file is called LCDDriver asm and can be downloaded from the lab website There will also be another 2014 Oregon State University ECE375 Manual Page 23 Section Three Data Manipulation and the LCD Display program file called LCDTest asm that utilizes every function described below You can download it for a sample of using the LCD LCD driver function definitions are provided below In order for any function call to work the stack pointer must be initialized prior to the function call LCDinit This subroutine initializes the seria
3. some type of expression These are known as pre compiler directives Define pre compiler directive What is the difference between the def and equ directives HINT see section 5 1 of the AVR Starter Guide given on the lab webpage 2 In this lab you were asked to manipulate data by moving it around in memory In fact the AVR architecture has two different memories a program memory and data memory Briefly explain the differences and purposes of these memories within your write up 3 You also learned how to make function calls Explain how the function call works its connection to the memory stack and why a RET instruction must be called to return from a function To help you understand comment out the stack pointer initialization in the beginning of the code and try running the program Observe and comment on this behavior CHALLENGE Not being content with displaying a static message you would like to add some flare by creating a scrolling marquee style message Your text will scroll across the lines from left to right When a character is at the end of a line it will be displayed at the beginning of the opposite line i e a character on slot 16 of line 1 will go to slot 1 of line 2 and a character on slot 16 of line 2 will go to slot 1 of line 1 You will also want to add a wait loop after all the characters have moved one slot so that you can read the characters Below is an example of the display and motion where signifies a spa
4. to the 3 element on the LCD display line Holds the line number that the char is going to be written to 1 or 2 mpr Contains the value of the ASCII char to be written 0 255 Example of writing D to Line 2 slot 7 2014 Oregon State University ECE375 Manual Page 25 Section Three Data Manipulation and the LCD Display ldi mpr D mpr lt D Ioi line 2 line lt 2 ldi count 7 count lt 7 reall LCDWriteByte Write Byte to LCD Display Bin2ASCIl This function will convert an unsigned 8 bit binary number into the numerically equivalent ASCII string i e 186 gt 186 For this function three registers are needed mpr Contains the 8 bit binary number to be converted X Pointer Contains the start address to AVR data memory when the ASCII string will be stored count Will contain the number of characters that are written once the function has completed This function is useful for printing a number that you don t always know what the value will be i e not a constant value such as a counter When using this function be aware that up to three characters could be written For example if you had the value 138 in the mpr and the address of 0112 in the X pointer you would get the following after calling this function DataMem 0112 1 DataMem 0113 3 DataMem 0114 8 count 3 Here is an example of calling the function described above
5. Section Three Data Manipulation and the LCD Display SECTION THREE Darta MANIPULATION AND THE LCD DISPLAY 2014 Oregon State University ECE375 Manual Page 21 Section Three Data Manipulation and the LCD Display SECTION OVERVIEW Complete the following objectives PR Create an AVR assembly project in AVR Studio Understand the basics of data manipulation Initialize a program i e stack registers LCD etc Use indirect addressing with the X Y and Z pointers Read data from program memory Move data around in data memory Setup and successfully call functions and subroutines ELAB The answers to the prelab questions can be found in the AVR Starters Guide and the AVR Instruction Set What is the stack pointer How is the stack pointer used and how do you initialize it Provide pseudo code NOT actual assembly code that illustrates how to initialize the stack pointer What does the AVR instruction LPM do and how do you use it Provide pseudo code that shows how to use the LPM instruction Look at the definition file m128def inc What is contained within this definition file What are the benefits of using this definition file How would you include it into your AVR Assembly program PROCEDURE Introduction For this lab you will learn to use the LCD Display on the AVR microcontroller board In order to use the LCD display you will need to learn to properly initialize your program You will also learn how to move data fr
6. a i e ASCII string that you want displayed on line 2 of the LCD display into the data memory addresses corresponding to line 2 and call the function Move ASCII string to line addresses 0110 S011F reall LCDWrLn2 Write string to LCD LCDClear This subroutine will clear both lines of the LCD display and the lines in AVR data memory will be cleared to the ASCII value of space No prior setup is required rcall LCDClear Clear both lines of LCD LCDCirLn1 This subroutine will clear line 1 of the LCD Display and line 1 in the AVR data memory in the same fashion as LCDClear No prior setup is required reall LCDClrLinl Clear line 1 LCDCirLn2 This subroutine will clear line 2 of the LCD display and line 2 in the AVR data memory in the same fashion as LCDClear No prior setup is required reall LCDC1lrLn2 Clear line 2 LCDWriteByte This function allows you to write a single ASCII character or byte anywhere on the LCD display This allows complete control over where things go within the display and does not require the AVR data memory lines as in the previous functions There are three registers that need to be initialized prior to calling this function count Holds the index value of the line to where the ASCII Char will be written 0 15 of 39 Indexes 0 15 are visible on the display but can be up to 39 thus indexes 16 39 are off screen If count has a value of 3 then the ACSII char will be written
7. ce 1 Line 1 My Name is Line 2 John Doe 2014 Oregon State University ECE375 Manual Page 28 Section Three Data Manipulation and the LCD Display wait 25sec 2 Line 1 My Name is Line 2 John Doe wait 25sec 3 Line 1 e My Name 1 Line 2 s John Do wait 25sec 4 Line 1 oe My Name Line 2 is John D wait 25sec etc Use the strings that are required for the lab to scroll Submit this code with your report Demonstrate the challenge problem to the TA for credit 2014 Oregon State University ECE375 Manual Page 29
8. e 3 With the current project activated in step 2 follow the Project Simulation tutorial in Section 2 1 3 of the AVR Starters Guide to learn how to compile and simulate your program By the end of this step you should know how to successfully create an AVR project from scratch and be able to compile it into usable program hex code 4 When assembly source code is compiled it creates a binary program file called a HEX file with a hex extension This HEX file contains the actual binary instructions that are used by the ATmega128 and is what needs to be uploaded onto the AVR Microcontroller Board Initialization A program initialization consists of any code that is only run once at the beginning of the program This code does not belong in the MAIN program this is why most Assembly programs begin with INIT and not MAIN The INIT function is not a function in the classic sense but rather a function that is called at reset and at power on and jumps to the main program once it is finished There are several things that should be contained in the INIT function The first and foremost is the initialization of the stack pointer The stack in AVR operates in a higher to lower address fashion meaning that the most recent element placed on the stack is in a lower address space than the previous element Therefore the stack should be initialized to the highest data address space available See the AVR Starters Guide for more information about the stack
9. l interface that is used to communicate with the LCD display initializes the Hitachi Display Chips with 8 bit Incremental DD RAM Pointer with no features and sets the display to 2x16 characters reall LCDInit Call LCD Init Subroutine LCDWrite This is a generic function that will write out both lines of text to the LCD display The line data is fetched from the following AVR data memory addresses Line 1 0100 010F Line 2 0110 011F In order to use this function you must first put the data i e ASCII string that you want displayed on the LCD in the appropriate line address in data memory Then call the function Move ASCII string to line addresses 0100 S011F reall LCDWrite Write string to LCD LCDWrLn1 This function will write the ASCII string stored in AVR data memory addresses 0100 010F to the first line of the LCD display To use this function you must first put the data i e ASCII string that you want displayed on line of the LCD display into the data memory addresses corresponding to line 1 and call the function Move ASCII string to line addresses 0100 SO010F reall LCDWrLnl Write string to LCD LCDWrLn2 This function will write the ASCII string stored in AVR data memory addresses 0110 011F to the second line of the LCD display 2014 Oregon State University ECE375 Manual Page 24 Section Three Data Manipulation and the LCD Display To use this function you must first put the dat
10. m Z Z DataMem Y lt mpr Y while Z End Address of string in Prog Memory Writing Your Name You are to write your name on the first line of the LCD Display and a simple phrase such as Hello World on the second line of the LCD Display In order to accomplish this you must have you two strings in program memory using the DB directive Then read the 2014 Oregon State University ECE375 Manual Page 27 Section Three Data Manipulation and the LCD Display data from program memory and store it into the appropriate spots in data memory that are used for Line and Line 2 Then make a simple call to the correct function to display the two lines on the LCD display You must first correctly initialize your program To help you along the process skeleton code is provided Use this as a starting point When you are finished demonstrate your LCD Display to the TA to get credit Have them sign below TA Signature STUDY QUESTIONS REPORT Write a short summary that details what you did and why explain any problems you may have encountered and answer the questions below Your write up should follow the required format given on the lab web page Submit a hard copy of your write up and code to your TA by the beginning of class the week following the lab NO LATE WORK IS ACCEPTED Study Questions 1 Take a look at the code you downloaded for today s lab Notice the lines that begin with def and equ followed by
11. om your program memory into your data memory This data is what will be displayed on the LCD display To help you along the way a project skeleton file will be provided This file will contain some code and comments directing you to what code to write and where The file will also give you a basis for writing well structured code as defined in the AVR Starters Guide Setup 1 Atmel Studio is the Integrated Development Environment IDE that you will be using to develop your AVR assembly code throughout the remainder of the course Atmel Studio is a powerful IDE created by Atmel for their line of AVR microcontrollers You will be using it to write assembly programs for your AVR microcontroller board that uses an ATmegal28 microcontroller Section 2 of the AVR Starter Guide which can be found on the lab website contains a good overview on how to use the program as well as some step by step tutorials Briefly read through this section to gain a basic understanding of the IDE 2014 Oregon State University ECE375 Manual Page 22 Section Three Data Manipulation and the LCD Display 2 Follow the steps in Section 2 1 2 in the AVR Starters Guide to create a new assembly project This will be very similar to the C project you created in Lab 1 In most IDE tools a project is the base starting area to your program It consists of all files you use and any settings for the program When following this tutorial you ll want to use the Lab 2 skeleton cod
12. te directive allows data to be written directly to the program memory during compilation For example the following code demonstrates how to create data in program space DATA DB 05 SF4 When the program is compiled the hex data 0x05 and OxF4 will be located in the program memory at the address specified by the label DATA To read this data use the LPM Load Program Memory instruction Note Since the program memory is 16 bits wide the data after the DB directive needs to be in multiples of 16 bits Otherwise the compiler will insert an extra byte of data usually FF The movement within data memory is accomplished with the different variations of Load and Store commands There are two main addressing modes to move the data direct addressing and indirect addressing Direct addressing is best when you want to move data to and from a single memory location like an extended I O register Indirect addressing uses the X Y and Z pointers and is useful for moving data to multiple areas of data memory For example using indirect addressing in conjunction with a while loop you could move blocks of data around in memory See the AVR Starters Guide for more information on pointers and indirect addressing The following is some pseudo code you can use to properly read a bunch of data from program memory Z lt Beginning Address of string in Program Memory Y lt Beginning Address in Data Memory for string do mpr lt ProgMe
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