Chapter 2: Assembly Language Programming The PIC18 ...

1 The PIC18 MicrocontrollerChapter 2: Assembly Language ProgrammingThe PIC18 MicrocontrollerHan-Way HuangMinnesota State University MankatoMinnesota State University, MankatoH. Huang Transparency @ 2005 Thomson Delmar LearningThe PIC18 MicrocontrollerComponents of an Assembly Program- Assembler directives- Assembly Language instructions- CommentsElements of an Assembly Language Statement- Label- MnemonicsOperands-Operands-CommentH. Huang Transparency @ 2005 Thomson Delmar LearningThe PIC18 MicrocontrollerLabel FieldLabel Field- Must start from column 1 and followed by a tab, a space, a colon (:), or theend of a Must start with an alphabetic character or underscore (_).-May contain alphanumeric characters underscores and question marks (?)-May contain alphanumeric characters, underscores and question marks (?).- May contain up to 32 characters and is case-sensitive by ,7; waitis a label_againdecfloop_cnt,F; _againis a labelH. Huang Transparency @ 2005 Thomson Delmar LearningThe PIC18 MicrocontrollerMnemonic FieldMnemonic Field- Can be an Assembly instruction mnemonic or Assembly directive- Must begin in column two or greater- Must be separated from the label by a colon, one or more spaces or tabsaddlw 0x10; addlw is the mnemonic fieldloopincf0x30,W,A; incf is a mnemonic falseequ0; equ is the mnemonic fieldH.

2 Huang Transparency @ 2005 Thomson Delmar LearningThe PIC18 MicrocontrollerThe Operand FieldThe Operand Field- The operand (s) follows the instruction Provides the operands for an instruction or arguments for an assembler Must be separated from the mnemonic field by one or more spaces or operands are separated by commasMultiple operands are separated by 0x30,0x400 ; 0x30,0x400 is the operand fielddecfloop_cnt,F; label loop_cntis the operandtrueequ1; 1 is the argument for equH. Huang Transparency @ 2005 Thomson Delmar LearningThe PIC18 MicrocontrollerComment field- Is optional- A comment starts with a All characters to the right of the semicolon are ignored by the assembler- Comments provide documentation to the instruction or assembler directives- A comment may explain the function of a single statement or the function ofa group of instructionstoo highdecfmean F A; prepare to search in the lower halftoo_highdecfmean,F,A; prepare to search in the lower half too_high is a label decf is a mnemonicdecf is a mnemonic mean,F,A is the operand field ; prepare to search in the lower half is a commentH.

3 Huang Transparency @ 2005 Thomson Delmar Learning ; prepare to search in the lower half is a commentThe PIC18 MicrocontrollerAssembler DirectivesAssembler Directives - Control directivesDt di ti-Data directives- Listing directives- Macro directives- Object file directivesH. Huang Transparency @ 2005 Thomson Delmar LearningThe PIC18 MicrocontrollerControl Directivesif<expr>; directives for conditional version == 100movlw D 10 movwf io1,Aelseelsemovlw D 26 movwf io2,Aendifend; indicates the end of the programH. Huang Transparency @ 2005 Thomson Delmar LearningThe PIC18 Microcontroller[<label>] code [<ROM address>][<label>] code [<ROM address>]-Declares the beginning of a section of program no label is specified, the section is named .code .-The starting address of the section is either included in the directive or assigned at link time if not specified in the #define <name> [<string>] ; defines a text substitution string#defineloop_cnt30#definesum3(x,y,z ) (x + y + z)#defineseed103#defineseed103#undefine <label>; deletes a substitution stringH.

4 Huang Transparency @ 2005 Thomson Delmar LearningThe PIC18 Microcontroller#include <include file> (or#include <include file>)#include <include_file> (or #include <include_file>)#include ; include the from current directory#include < >; include the file the installation; directory of <default_radix>- sets the default radix for data expressionth d f ltdilhdt-the default radix values are: hex, dec, or octradixdec; set default radix to decimalH. Huang Transparency @ 2005 Thomson Delmar LearningThe PIC18 Microcontrollerwhile <expr>pendw- The lines between whileand endware assembled as long as <expr>is Directivesdb<expr> <expr>; define 1 or multiple byte valuesdb <expr>,..,<expr>; define 1 or multiple byte valuesdb text_string ; define a stringdw<expr>,..,<expr>; define 1 or multiple word constants dw text_string ; define a stringdt<expr>, .., <expr>; generates a series of retlw instructions<label> set<expr>; assign a value (<expr>) to label<label> equ<expr>; defines a constantH.

5 Huang Transparency @ 2005 Thomson Delmar LearningThe PIC18 MicrocontrollerData Directives ExamplesData Directives Examplesled_pat db0x30,0x80,0x6D,9x40,0x79,0x20,0x33,0x1 0,0x5B,0x081db Plh i(1/2) 0msg1db Please enter your choice (1/2): ,0arraydw0x1234,0x2300,0x40,0x33msg2dw The humidity is ,0results dt1,2,3,4,5sum_hi set0x01sum_lo set0x00 THequ200 TLequ30H. Huang Transparency @ 2005 Thomson Delmar LearningTLequ30 The PIC18 MicrocontrollerWhat is a macro?What is a macro?-A group of instructions that are grouped together and assigned a name-One or multiple arguments can be input to a macro-By entering the macro name, the same group of instructions can be duplicated in any place of the program is made more readable by using macrosUser becomes more productive by saving the text entering time-User becomes more productive by saving the text entering timeMacro DirectivesmacroendmexitmH. Huang Transparency @ 2005 Thomson Delmar LearningThe PIC18 MicrocontrollerMacro Definition Exampleseeritualmacro; macro name is eeritualmovlw 0x55; instruction 1 movwfEECON2; instruction 2movwfEECON2; instruction 2movlw 0xAA; instruction 3movwf EECON2; instruction 4endmMacro Call Exampleeeritual; this macro call causes theeeritual; this macro call causes the; assembler to insert; instruction 1.

6 Instruction 4H. Huang Transparency @ 2005 Thomson Delmar LearningThe PIC18 MicrocontrollerMore Macro Examplessum_of_3macro arg1, arg2, arg3; WREG [arg1]+[arg2]+[arg3]movfarg1,W,Aaddwfarg 2,W,Aaddwf arg3,W,Aendmendmsum_of_30x01, 0x02, 0x03; WREG [0x01] + [0x02] + [0x03]H. Huang Transparency @ 2005 Thomson Delmar LearningThe PIC18 MicrocontrollerObject File Directivesjbanksel <label>hiii d b k hh-generate the instruction sequence to set active data bank to the one where<label> is located-<label> must have been defined before the banksel directive is ditiillthbltbankselbigq; this directive will cause the assembler to ; insert the instruction movlb 0x03H. Huang Transparency @ 2005 Thomson Delmar LearningThe PIC18 MicrocontrollerObject File Directives (continues)Object File Directives (continues)[<label>] org<expr>- sets the program origin for subsequent code at the address defined in <expr>.- <label> will be assigned the value of <expr>. ; led_pathas the value of 0x1000db0x7E,0x30,0x6D,0x79,0x33,0x5B,0x 5F,0x70,0x7F,0x7BH.

7 Huang Transparency @ 2005 Thomson Delmar LearningThe PIC18 MicrocontrollerObject File Directives (continued)Object File Directives (continued)processor<processor_type>Sh-Sets the processor typeprocessor p18F8680; set processor type to PIC18F8680H. Huang Transparency @ 2005 Thomson Delmar LearningThe PIC18 MicrocontrollerProgram Development ProcedureProgram Development Procedure - Problem definition - Algorithm development using pseudo code or flowchart- Converting algorithm into Assembly instruction sequence- Testing program using normal data, marginal data, and erroneous dataAlgorithm RepresentationStep 3H. Huang Transparency @ 2005 Thomson Delmar PIC18 MicrocontrollerFlowchart SymbolsFlowchart SymbolsTerminalAProcessSubroutineInput oroutputBoff-page connectorDecisionyesnoAon-page connectorFigure Flowchart symbols used in this bookH. Huang Transparency @ 2005 Thomson Delmar LearningThe PIC18 MicrocontrollerAblPTlAssembly Program Templateorg 0x0000; program starting address after power on resetgoto startgorg ; high-priority interrupt service routineorg0x18; lowpriority interrupt service ; low-priority interrupt service ; your programendH.

8 Huang Transparency @ 2005 Thomson Delmar LearningThe PIC18 MicrocontrollerProgram Template Before Interrupts Have Been Coveredorg 0x0000; program starting address after power on resetgoto startgoto startorg 0x08retfie; high-priority interrupt service routineorg0x18tfi li it i tt i tiretfie; low-priority interrupt service ; your programendH. Huang Transparency @ 2005 Thomson Delmar LearningThe PIC18 MicrocontrollerCase Issue- The PIC18 instructions can be written in either uppercase or MPASM allows the user to include file to provide register definitions for the specific processordefinitions for the specific All special function registers and bits are defined in The convention followed in this text is: using lowercasefor instructions and directives, using uppercasefor special function Huang Transparency @ 2005 Thomson Delmar LearningThe PIC18 MicrocontrollerByte Order IssueByte Order Issue- This issue concerns how bytes are stored for multi-byte The big-endianmethod stores the most significant byte at the lowest address and stores the least significant byte in the highest The little-endianmethod stores the most significant byte of the number at the highest address and stores the least significant byte of the number in the lowest The 32-bit number 0x12345678 will stored as follows with two methods:Big-Endian MethodLittle-Endian MethodaddressPP+1P+2P+3PP+1P+2P+3value12 34567878563412(in hex)Figure 02 t1 Byte order exampleH.

9 Huang Transparency @ 2005 Thomson Delmar LearningFigure 02_t1 Byte order exampleThe PIC18 MicrocontrollerPrograms for Simple Arithmetic OperationsPrograms for Simple Arithmetic OperationsExample Write a program that adds the three numbers stored in data registers at 0x20, 0x30, and 0x40 and places the sum in data register at :Algorithm:Algorithm:Step 1 Load the number stored at 0x20 into the WREG 2 Add the number stored at 0x30 and the number in the WREG register and leave the sum in the WREG 3pAdd the number stored at 0x40 and the number in the WREG register and leave the sum in the WREG 4 Store the contents of the WREG register in the memory location at 0x50H. Huang Transparency @ 2005 Thomson Delmar LearningStore the contents of the WREG register in the memory location at PIC18 MicrocontrollerThe program that implements this algorithm is as follows:The program that implements this algorithm is as follows:#include < > ; can be other processor org0x00gotostartorg0x08retfieretfieorg0x 18retfiestartmovf0x20,W,A; WREG [0x20]addwf0x30,W,A; WREG [0x20] + [0x30]addwf0x40,W,A; WREG [0x20] + [0x30] + [0x40]movwf 0x50,A; 0x50 sum (in WREG)endH.

10 Huang Transparency @ 2005 Thomson Delmar LearningendThe PIC18 MicrocontrollerExample a program to add two 24-bit numbers stored at 0x10~0x12 andExample a program to add two 24bit numbers stored at 0x10 0x12 and 0x13~0x15 and leave the sum at :#include < >org0x00org0x00gotostartorg0x08retfieorg0 x18org0x18retfiestartmovf0x10,W,A; WREG [0x10]addwf0x13,W,A; WREG [0x13] + [0x10]f020A020 [0 10] + [0 13]movwf0x20,A; 0x20 [0x10] + [0x13]movf0x11,W,A; WREG [0x11]addwfc0x14,W,A; WREG [0x11] + [0x14] + C flagmovwf0x21,A; 0x21 [WREG]movf0x12,W,A; WREG [0x12]addwfc0x15,W,A; WREG [0x12] + [0x15] + C flagmovwf0x22,A; 0x22 [WREG]endH. Huang Transparency @ 2005 Thomson Delmar LearningendThe PIC18 MicrocontrollerExample Write a program to subtract 5 from memory locations 0x10 toExample Write a program to subtract 5 from memory locations 0x10 to :AlithAlgorithm:Step 1. Place 5 in the WREG 2. Subtract WREG from the memory location 0x10 and leave the difference pyin the memory location 3.