ECE 265 – Lecture 9

1. ECE265 ECE 265 – Lecture 9 PROGRAM DESIGN

2. Lecture Overview • Program Design • General Overview • Program Design Methodology • Assembler Language • Assembler Directives • REF: Chapter 4 ECE265

3. Program Design • General Overview • From the text page 89: “The design of an embedded microcontroller system requires an integrated use of hardware and software.” • Hardware and software provide a natural division of the view of the system. Embedded systems require well designed interaction between these two divisions. • The software design needs to follow established methodologies. ECE265

4. Software Design Methodology • The software of the system is typically called a Software Program. • A software program is software compiled and assembled into executable code for the target machine. • Window7 is a program designed as the operating system for general purpose PCs and will run on hardware structured to support that OS. ECE265

5. Top-down design methodology • A popular design methodology for software is Top-Down design and Bottom-up coding. • It starts with a specification of the system at the top level. • This top-level is then broken down into major tasks and subtasks. • Each major task (and subtask) is broken down into smaller subtasks as appropriate. ECE265

6. Top-Down Design • Graphical illustration of the Top-down design methodology. • The number of levels continues until the subtask is one that can be directly coded. ECE265

7. Benefits of the top-down method • Each subtask is independent of other subtasks, allowing the programmer to design, write and test each module independently. • Errors can be detected and corrected in a logical manner. • Mentally, the programmer only has to grasp one subtask at a time. • A team of programmer can be used to accomplish the project faster. • Program modules can be used in future applications. For example, your program needs to use a linked list data structure. Most likely the routines to manage and manipulate a linked list are available. ECE265

8. Statement of the problem • Where it all starts. • The highest level of abstraction • The statement of the problem to be solved • Requires full analysis of the problem to be addressed and the system being designed to address it. ECE265

9. An example of the methodology • Example 4.2 from the Text. ECE265

10. Assembler language programming • A good practice is never to program in assembler language directly. • Start with the specification of the module to be coded. • Code it in a Pseudo Design Language or PDL • PDL is much like any high level programming language. ECE265

11. Assembler Language • Assembler Language is specific to the machine (processor architecture). • Each processor version may have instructions that other versions do not have. • Assembler language has a 1-to-1 relationship with the machine language, i.e., executable code of the processor. • One assembler language statement • = • one executable instruction. ECE265

12. Assembler language • Usually written line by line where each line is 80 character long. • Within the 80 character line there are fields. Field position can be fixed. For example: • The first 10 characters are a label • The next field is for the operand or assembler directive • This is followed by the operand field • The last filed is for comments ECE265

13. The 68HC11 format • Each assembler language statement is on one line • Starts in column 1 and has 4 fields • The label field • The op code field • The operand filed • The comment field • THE LABEL FIELD • Starts in column 1 • Can be blank • Label can be up to 15 characters in length • Upper case is distinct from lower case and must start with a character • TDREG1 is valid 1TDREG is not valid • Delimited (ended) by a ‘:’ or a ‘ ’ ECE265

14. The 68HC11 format (cont) • The operation field • Must start in column 2 or after • Best to start in the same column for the complete program • Contains the instruction mnemonic such a LDAA, OR • an assembler directive OR • a macro call • Operand Field • The field contains the instruction operand or argument for assembler directives • Numbers in this field are identified by some symbols that can precede the number • None A decimal number • $ The number is a hexidecimal number • @ The number is an octal number • % The number is a binary number ECE265

15. 68HC11 formal continued • The comment field • The last field is a comment field and is separated from the previous filed by at least one space • An optional field • Can have any printable ASCII character as this field is used for documentation • Can be continued (or you can use any line as a comment) by starting the line with a *. These lines are considered as comments and anything on the line is considered a comment, i.e., no assembly takes place. • LABEL: OPCODE OPERAND COMMENT ECE265

16. Assembler directives • These are direction to the assembler to perform a particular task or set up a specific condition. • The assembler directives are ECE265

17. NAM directive • Give the program a name. • Documentation only. There is no impact on the machine code generated. • NAM Pressure Monitoring ECE265

18. ORG directive • Used extensively and common to all assemblers. • Sets the location (physical location) counter to a set value. • Example • ORG $C000 • CNTMAX RMB 2 • This would place the 16-bits for CNTMAX at address $C000 and 2 bytes of memory are set aside. • ORG $D000 • START LDAA #$46 • x • x • Here the ORG place the executable code to start at address $D000 and the label START would have a value of $D000 • Memory address $D000 contains $86, • the op code for LDAA immediate mode ECE265

19. END directive / EQU directive • END simply indicates that this is the last source code line. • EQU allows a value to be given to label for more readable and understandable code. • <label> EQU <expression> [<comment>] • EX • ADCTL EQU $1030 Location of the A/D control • register. ECE265

20. FCB directive • Form Constant Byte • This directive can have more than one value in the operand field. • EX • DIGITS FCB 0, 1, 2, 3 Fills a 4-byte memory • buffer labeled with DIGITS • with values 0,1,2, and 3 • MYHEX FCB $32 Fills the location MYHEX • with a value of $32. ECE265

21. FCC directive • FCC is much like FCB except that now the memory locations are filled with the ASCII code for the characters in the string. • [<label>] FCC ‘<ASCII string>’ • Note the use of single ’s • Example • MYLAB FCC ‘my ASCII string’ ECE265

22. RMB • RMB with reserve space in memory and attach a label to that location that can be used in the assembler code to refer to the location. Does not affect the value in the location. • EX • MRCNT RMB 1 Reserve 1 byte • TREG1 RMB 2 Reserve 2 bytes • TEBUFF RMB 12 Reserve 12 bytes ECE265

23. SET directive • The SET directive established the value for a label being used in the assembler code. • <label> SET <expression> • EX • COUNT SET #40 sets the value for the label • COUNT to 40. Any time COUNT • is used it is the same as using 40 • If you later reassign a value to the label, that value will be the new value for the label. ECE265

24. BTEXT and ETEXT Directives • These directives allows the programmer to insert blocks of text easier than with the other directives. • No need for starting and ending quotes on each line • EXAMPLE • BTEXT • These lines will be ignored • by the assembler • but will appear in the LST file. • ETEXT • A BTEXT must be ended by a ETEXT ECE265

25. Lecture summary • Program Design • General Overview of software • Program Design Methodology • Assembler Language in general • Assembler Directives for the 68HC11 ECE265

26. Assignment • Problems : Chapter 4 page 127 – Prob 7 ECE265