4.5.1) The Label Field ) The Mnemonic Field. 4.5) Assembly Language Program Structure A PIC18 ALP consists of 3 type of statements:

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1 4.5) Assembly Language Program Structure A PIC18 ALP consists of 3 type of statements: 1) Assembler Directives To control the assembler: its input, output, and data allocation. Must be terminated with an END directive. Any statement after the END directive will be ignored by the assembler. 2) Assembly Language Instructions The PIC18 instructions. Up to 77 different instructions. 4.5) Assembly Language Program Structure (Cont.) Each line of the source file may consist of up to 4 fields: Label Mnemonic Operand Comment Statement fields are separated by blanks Tabs are allowed too. Label a Symbol whose first character is in column 1. Mnemonic instruction Mnemonic (Opcode) or Assembler Directive. Operand can be empty, a symbol, a number, or an expression. Comment the remainder of the line, may be blank. 3) Explain and document the function of a single or a group of instructions. 26 Example: loop addwf x2,f,a ;This is an example of ALP ) The Label Field 4.5.2) The Mnemonic Field Must start from column 1 and followed by a tab, a space, a colon (:), or the end of a line. Can be an assembly instruction mnemonic (operation code, Opcode) or assembler directive. Must start with an alphabetic character or underscore (_). May contain alphanumeric characters, underscores and question marks (?). Must begin in column two or greater. Must be separated from the label by a colon, one or more spaces or tabs. May contain up to 32 characters and is case-sensitive by default. wait btfss sum,7 ; wait is a label _again decf loop_cnt,f ; _again is a label false equ ; equ is an assembler directive addlw x1 ; addlw is the mnemonic loop incf x3,w,a ; incf is the mnemonic Lecturer: Dr Jamaludin Bin Omar 4-1

2 4.5.3) The Operand Field The operand(s) follows the instruction mnemonic. Provides the operands for an instruction or arguments for an assembler directive. Must be separated from the mnemonic field by one or more spaces or tabs. Multiple operands are separated by commas. movff x3,x4 ; x3,x4 is the operand decf loop_cnt,f ; label loop_cnt is the operand true equ 1 ; 1 is the operand for equ 3 Comment field is optional. A comment starts with a semicolon. All characters to the right of the semicolon are ignored by the assembler. provide documentation to the instruction or assembler directives. A comment may explain the function of a single statement or the function of a group of instructions. Example: 4.5.4) The Comment Field too_high decf mean,f,a ; prepare to search in the lower half too_high is a label decf is a mnemonic mean,f,a is the operand field ; prepare to search in the lower half is a comment ) Example of PIC18 ALP 4.6) Assembler Directives Identify the 4 fields of in the following source statement. Example: too_low addlw x2 ;increment WREG by 2 (1) (2) (3) (4) Tell the assembler to do something other than creating the machine code for an instruction. Provide the assembly language programmer with a means to instruct the assembler how to process subsequent assembly language instructions. Also provide a way to define program constants and reserve space for dynamic variables. (1) too_low is a Label (2) addlw is an Instruction Mnemonic (3) x2 is the Operand (4) ;increment WREG by 2 is a Comment 32 MPASM provides 5 types of directives: 1) Control directives: Permits sections of conditionally assembled code. 2) Data directives: Control the allocation of memory and provide a way to refer to data items symbolically using names. 3) Macro directives: Control the execution and data allocation within macro body definitions. 4) Listing directives: Control listing format i.e. titles, pagination, etc. 5) Object file directives: Used only when creating an object file. 33 Lecturer: Dr Jamaludin Bin Omar 4-2

3 CODE Begin executable code section [<name>] code [<address>] #DEFINE Define a text substitution section #define <name> [<value>] #define <name> [<arg>,..,<arg>] <value> ELSE Begin alternative assembly block to IF else END End program block end ENDIF End conditional assembly block endif ENDW End a while loop endw IF 1) Control directives, used to conditionally assembling the code, are listed in Table 2.1. Table 2.1 Begin conditionally assembled code block if <expr> IFDEF Execute if symbol has been defined ifdef <label> IFNDEF Execute if symbol has not been defined ifndef <label> #INCLUDE Include additional source code #include <<include_file>> <include_file> RADIX Specify default radix radix <default_radix> #UNDEFINE Delete a substitution label #undefine <label> WHILE Perform loop while condition is true while <expr> 34 1) Commonly used Control directives are: END End program block end #INCLUDE Include additional source code #include <<include_file>> <include_file> RADIX Specify default radix radix <default_radix> end ; Indicates the end of the program Example: list p=xxxx ;xxxx is the device name.. ;executable code.. end ;end of program 35 1) Commonly used Control directives are: END End program block end #INCLUDE Include additional source code #include <<include_file>> <include_file> RADIX Specify default radix radix <default_radix> #include <include_file> or #include <include_file> Includes additional source file #include lcd_util.asm from current directory ; include the lcd_util.asm file 1) Commonly used Control directives are: END End program block end #INCLUDE Include additional source code #include <<include_file>> <include_file> RADIX Specify default radix radix <default_radix> radix <default_radix> Sets the default radix for data expression Default radix values are: hex, dec, or oct Example: #include <p18f868.inc> ; include the file p18f868.inc from the installation directory of MPASM 36 radix dec ; set default radix to decimal 37 Lecturer: Dr Jamaludin Bin Omar 4-3

4 The user can choose his/her preferred radix to represent the number. MPASM supports the radices listed in Table 2.3. Table 2.3: MPASM radix specification Type Syntax Example Decimal D <decimal digits> D 1 Hexadecimal H <hex digits > x<hex digits> H 234D xc Octal O <octal digits> O 1357 Binary B <binary digits> B 111 ASCII <character> A <character> T A T 38 2) Data directives are listed in Table 2.2. Table 2.2 CBLOCK Define a block of constant cblock [<expr>] CONSTANT Declare symbol constant constant <label> =<expr>[.., <label> =<expr>] DA Store strings in program memory [<label>] da <expr>[, <expr>,.., <expr>] DATA Create numeric and text data [<label>] data <expr>[, <expr>,.., <expr>] [<label>] data <text_string> [, <text_string>,..] DB Declare data of one byte [<label>] db <expr>[, <expr>,.., <expr>] [<label>] db <text_string> [, <text_string>,..] DT Define table [<label>] dt <expr>[, <expr>,.., <expr>] [<label>] dt <text_string> [, <text_string>,..] DW Declare data of one word [<label>] dw <expr>[, <expr>,.., <expr>] [<label>] dw <text_string> [, <text_string>,..] ENDC End an automatic constant block endc EQU Define an assembly constant <label> equ <expr> FILL Fill memory [<label>] fill <expr>,<count> RES Reserve memory [<label>] res <mem_units> SET Define an assembler variable <label> set <expr> VARIABLE Declare symbol variable variable <label>[=<expr>,.., <label>[=<expr>]] 39 2) Commonly used Data directives are: CONSTANT Declare symbol constant constant <label> =<expr>[.., <label> =<expr>] DATA Create numeric and text data [<label>] data <expr>[, <expr>,.., <expr>] [<label>] data <text_string> [, <text_string>,..] DB Declare data of one byte [<label>] db <expr>[, <expr>,.., <expr>] [<label>] db <text_string> [, <text_string>,..] DW Declare data of one word [<label>] dw <expr>[, <expr>,.., <expr>] [<label>] dw <text_string> [, <text_string>,..] EQU Define an assembly constant <label> equ <expr> RES Reserve memory [<label>] res <mem_units> 2) Commonly used Data directives are: constant <label> = <expr> [.., <label> = <expr>] Creates symbols for used in MPASM expressions. Constants may not be reset after being once been initialized, and the expression must be fully resolvable at the time of the assignment. Example: constant duty_cycle = D 5 4 will cause 5 to be used whenever the symbol duty_cycle is encountered in the program. 41 Lecturer: Dr Jamaludin Bin Omar 4-4

5 2) Commonly used Data directives are: [<label>] data <expr>[,<expr>,..,<expr>] [<label>] data <text_string> [, <text_string> ] The data directive initializes one or more words of program memory with data. Each <expr> is stored in one word. The data may also consist of ASCII character strings, <text_string>, enclosed in a single quotes for one character or double quotes for strings. Example: data 1,2,3 ;constants data count from 1,2,3 ;text string data A ;single character data main ;relocatable label 42 2) Commonly used Data directives are: [<label>] db <expr>[,<expr>,..,<expr>] The db directive reserves program memory words with packed 8-bit values. Multiple expressions continue to fill bytes consecutively until the end of expressions. Should there be an odd number of expressions, the last byte will be zero. When generating an object file, this directive can also be used to declare initialized data values. Example: db b,x22, t,x1f, s,x3, t, \n 43 2) Commonly used Data directives are: [<label>] dw <expr>[,<expr>,..,<expr>] This directive reserves program memory words for data, initializing that space to specific values. Values are stored into successive memory locations, and the location is incremented by one. Expressions may be literal strings and are stored as described in the data directive. 2) Commonly used Data directives are: [<label>] equ <expr> The equ directive defines a constant. Whenever the label appears in the program, the assembler will replace it with <expr>. Example: Example: dw dw 39,24, display data array_cnt-1 44 true equ 1 false equ four equ 4 45 Lecturer: Dr Jamaludin Bin Omar 4-5

6 2) Commonly used Data directives are: [<label>] res <mem_units> The MPASM uses a memory location pointer to keep track of the address of the next memory location to be allocated. This directive will cause the memory location pointer to be advanced from its current location by the value specified in <mem_units> Example: buffer res 64 3) Macro directives, used to control the execution and data allocation within macro body definitions, are listed in Table 2.4. Table 2.4 ENDM End of a macro definition endm EXITM Exit from a macro exitm MACRO Declare macro definition <label> macro [<arg>,..,<arg>] EXPAND Expand macro listing expand LOCAL NOEXPAND Declare local macro variable Turn off macro expansion local <label> [, <label>] noexpand ) Commonly used Macro directives are: ENDM End of a macro definition endm EXITM Exit from a macro exitm MACRO Declare macro definition <label> macro [<arg>,..,<arg>] 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. User program is made more readable by using macros. User becomes more productive by saving the text entering time. 48 3) Commonly used Macro directives are: <label> macro [<arg>,.., <arg>] endm A name (i.e. <label>) is required for the macro definition. To invoke the macro, specify the name and the arguments of the macro, the assembler will insert the instruction sequence between the macro and endm directives into the program. Example sum_of_3 macro arg1,arg2,arg3 movf arg1,w,a addwf arg2,w,a addwf arg3,w,a endm 49 Lecturer: Dr Jamaludin Bin Omar 4-6

7 3) Commonly used Macro directives are: Example (Cont.) If the user wants to add three data registers at x2, x21, and x22 and leave the sum in WREG, the user can use the following statement to invoke the previous macro: sum_of_3 x2,x21,x22 When processing this macro call, the assembler will insert the following instructions in the user program: movf x2,w,a addwf x21,w,a addwf x22,w,a 5 3) Commonly used Macro directives are: <label> macro exitm [<arg>,.., <arg>] endm A This name directive (i.e. <label>) forces immediate is required return for the from macro micro definition. To expansion invoke the during macro, assembly. specify The the effect name is and the the same arguments as if an of endm the macro, directive the had assembler been encountered. will insert the instruction sequence Example between the macro and endm directives into the test program. macro arg1 Example if arg1 == 3 ;check for valid file register sum_of_3 macro arg1,arg2,arg3 exitm movf else arg1,w,a addwf arg2,w,a error bad file assignment addwf endif arg3,w,a endm 51 4) Listing directives, used to control the MPASM listing file format, are listed in Table 2.5. For more details, refer to Huang, page 49-5! Table 2.5 ERROR Issue an error message error <text_string> ERRORLEVEL Set error level errorlevel 1 2<+ -><message number> LIST Listing options list [<list_option>,.., <list_option>] MESSG Create user defined message messg <message_text> NOLIST Turn off listing options nolist PAGE Insert listing page eject page SPACE Insert blank listing lines space <expr> SUBTITLE Specify program subtitle subtitle <sub_text> TITLE Specify program title title <title_text> 52 5) Object File directives, used in controlling the generation of object code, are listed in Table 2.8. Table 2.8 BANKSEL Generate RAM bank selecting code banksel <label> CODE Begin executable code section [<name>] code [<address>] _CONFIG Specify configuration bits _config <expr> OR _config <addr>,<expr> EXTERN Declare an external label extern <label>[,<label>] GLOBAL Export a defined label global <label>[,<label>] IDATA Begin initialized data section [<name>] idata [<address>] ORG Set program origin <label> org <expr> PROCESSOR Set processor type Processor <processor_type> UDATA Begin uninitialized data section [<name>] udata [<address>] UDATA_SHR Begin shared uninitialized data section [<name>] udata_shr [<address>] 53 Lecturer: Dr Jamaludin Bin Omar 4-7

8 5) Commonly used Object Files directives, used in controlling the generation of object code, are: CODE Begin executable code section [<name>] code [<address>] EXTERN Declare an external label extern <label>[,<label>] GLOBAL Export a defined label global <label>[,<label>] ORG Set program origin <label> org <expr> PROCESSOR Set processor type Processor <processor_type> 5) Commonly used Object Files directives, used in controlling the generation of object code, are: [<label>] code [<ROM address>] Declares the beginning of a section of program code. If 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 directive. 54 reset code x goto start Creates a new section called reset starting at address x. The 1 st instruction is goto start 55 5) Commonly used Object Files directives, used in controlling the generation of object code, are: extern <label>[,<label>,..] 5) Commonly used Object Files directives, used in controlling the generation of object code, are: global <label>[,<label>,..] Declare symbols names that may be used in the current module but are defined as global in a different module. The external statement must be included before <label> is used. At least one label must be specified on the line. extern call function_x function_x 56 Declares symbol names that are defined in the current module and should be available to other modules. The directive must be used after <label> is defined. At least one label must be included. udata ax res 1 bx res 1 global ax,bx code addlw 3 57 Lecturer: Dr Jamaludin Bin Omar 4-8

9 5) Commonly used Object Files directives, used in controlling the generation of object code, are: [<label>] org [<expr>] Sets the program origin for subsequent code at the address defined in <expr>. If no org is specified, code generation will begin at zero. 5) Commonly used Object Files directives, used in controlling the generation of object code, are: processor Sets the processor type. processor <processor_type> p18f872 reset org x ;reset vector code goto start org x1 start ;code of our program ) The PIC18 Instruction Set: According to machine code production There are 5 categories: 1) Literal operations 2) Byte-oriented operations 3) Bit-oriented operations 4) Control operations 5) Data memory Program memory operations Note: Most instructions are a single program memory word (16-bits), but there are some instructions that require two program memory locations. Each single word instruction consists of an OPCODE and one or more OPERANDS 6 A literal value (specified by k ) to be operated on or loaded into a file register or WREG The desired FSR register to load the literal value into (specified by f ) For example: movlw x1f 4.7.1) Literal operations opcode k = 8-bit immediate value 8 Figure 1.11 Literal operations (redraw with permission of Microchip) 7 k 61 Lecturer: Dr Jamaludin Bin Omar 4-9

10 4.7.1) Literal operations (Cont.) 4.7.2) Byte-oriented operations Operate on any Data Memory specified by the 8-bit address f For example: movwf x255, A opcode d a f d = for result destination to be WREG register. d = 1 for result destination to be file register (f) a = to force Access Bank a = 1 for BSR to select bank f = 8-bit file register address Figure 1.8 Byte-oriented file register operations (redraw with permission of Microchip) ) Byte-oriented operations (Cont.) 4.7.2) Byte-oriented operations (Cont.) Lecturer: Dr Jamaludin Bin Omar 4-1

11 4.7.3) Bit-oriented operations Operate on any single bit b in f For example: bcf PORTB, 3, A o p c o d e b a f 8 b = 3 -b it p o s itio n o f b it in th e file registe r (f). a = to force Access Bank a = 1 for BSR to select bank f = 8 -bit file register address Figure 1.1 Bit-oriented file register operations (redraw w ith perm ission of M ic ro c h ip ) 7 These instructions are used to change the program execution sequence and making subroutine calls 4.7.4) Control operations opcode 1111 n<19:8> (literal) n = 2-bit immediate value opcode 1111 n<19:8> (literal) S = fast bit opcode opcode S n<7:> (literal) n<7:> (literal) n<1:> (literal) n<7:> (literal) GOTO label CALL funct_name BRA label BC label 66 Figure 1.12 Control operations (redraw with permission of Microchip) ) Control operations (Cont.) 4.7.5) Data memory Program memory operations For handling data transfer between data memory and program memory Lecturer: Dr Jamaludin Bin Omar 4-11

12 4.8) The PIC18 Instruction Set: According to operation performed 1) Data transfer operations 2) Data manipulation operations Arithmetic Increment and decrement Logic Rotate 3) Program control operations Create a condition Check if the condition is met Branch or skip 4) Data memory Program memory operations ) Data Transfer Operations Data Transfer Instructions MOVLW k Move literal to WREG k is a 8-bit literal number MOVLB k Move literal to low nibble of BSR LFSR i,k Load FSRi with literal k, when i = ~2 k is a 12-bit literal number Use to set the FSR k is a 4-bit literal number Use to set the BSR MOVF f,d,a Move f to somewhere Default: d=file, a=banked MOVFF fs,fd Move fs to fd 2-word, 2-cycle instruction Either fs or fd can be WREG MOVWF f,a Move WREG to f Default: a=banked ) Data Manipulation Operations 4.8.2) Data Manipulation Operations (Cont.) a) Arithmetic b) Increment and Decrement Arithmetic Instructions NEGF f,a Negate f Default: a=banked Two s complement form ADDLW k Add WREG to literal k is a 8-bit literal number ADDWF f,d,a Add WREG to f Default: d=file, a=banked ADDWFC f,d,a Add WREG and C bit to f Default: d=file, a=banked SUBLW k Subtract literal from WREG k is a 8-bit literal number SUBWF f,d,a Subtract WREG from f Two s complement form Default: d=file, a=banked SUBWFB f,d,a f - WREG C (borrow) Default: d=file, a=banked SUBFWB f,d,a WREG f C (borrow) Default: d=file, a=banked Increment and Decrement Instructions INCF f,d,a Increment f Default: d=file, a=banked INCFSZ f,d,a Increment f, skip if Skip = skip next instruction Default: d=file, a=banked INFSNZ f,d,a Increment f, skip if not Skip = skip next instruction Default: d=file, a=banked DECF f,d,a Decrement f Default: d=file, a=banked DECFSZ f,d,a Decrement f, skip if Skip = skip next instruction Default: d=file, a=banked DCFSNZ f,d,a Increment f, skip if not Skip = skip next instruction Default: d=file, a=banked MULLW k Multiply WREG with k Result in PRODH:PRODL MULW f,a Multiply WREG with f Result in PRODH:PRODL WREG and f unchanged Lecturer: Dr Jamaludin Bin Omar 4-12

13 4.8.2) Data Manipulation Operations (Cont.) Logic Instructions CLRF f,a Clear register f Default: a=banked SETF f,a Set register f Default: a=banked COMF f,d,a Bitwise complement register f Default: d=file, a=banked ANDLW k Bitwise AND literal with WREG k is a 8-bit literal number ANDWF f,d,a Bitwise AND WREG with f Default: d=file, a=banked IORLW k Bitwise OR literal with WREG k is a 8-bit literal number IORWF f,d,a Bitwise OR WREG with f Default: d=file, a=banked XORLW k c) Logic Bitwise exclusive OR literal with WREG k is a 8-bit literal number XORWF f,d,a Bitwise ex-or WREG with f Default: d=file, a=banked 4.8.2) Data Manipulation Operations (Cont.) d) Rotate Rotate Instructions RLCF f,d,a Rotate left f with carry Default: d=file, a=banked RLNCF f,d,a Rotate left f without carry Default: d=file, a=banked RRCF f,d,a Rotate right f with carry Default: d=file, a=banked RRNCF f,d,a Rotate right f without carry Default: d=file, a=banked SWAPF f,d,a Swap nibbles in f Default: d=file, a=banked ) Program Control Operations a) Create a condition (e.g., operations that changes the status register, compare two numbers {more, less, or equal}, etc.) Byte Compare Instructions TSTFSZ f,a Test register f, skip if Default: a=banked CPFSEQ f,a CPFSGT f,a CPFSLT f,a Compare f with WREG, skip if = Compare f with WREG, skip if > Compare f with WREG, skip if < Default: a=banked Default: a=banked Default: a=banked CPFXXX instructions perform an unsigned subtraction, and then test the zero and sign flags ) Program Control Operations (Cont.) b) Check if the condition is met Bit Set and Test Instructions BCF f,b,a Clear bit f<b> Default: a=banked BSF f,b,a Set bit f<b> Default: a=banked BTG f,b,a Toggle bit f<b> Default: a=banked BTFSC f,b,a Test bit f<b>, skip if clear Default: a=banked BTFSS f,b,a Test bit f<b>, skip if set Default: a=banked 77 Lecturer: Dr Jamaludin Bin Omar 4-13

14 4.8.3) Program Control Operations (Cont.) c) Branch or skip Branch Instructions BRA n Unconditional branch N is 11-bit signed offset BC n Branch if carry N is 11-bit signed offset BNC n Branch if no carry N is 11-bit signed offset BN n Branch if negative N is 11-bit signed offset BNN n Branch if not negative N is 11-bit signed offset BOV n Branch if overflow N is 11-bit signed offset BNOV n Branch if not overflow N is 11-bit signed offset BZ n Branch if zero N is 11-bit signed offset BNZ n Branch if not N is 11-bit signed offset Note: The assembler will calculate the offset ) Program Control Operations (Cont.) Example n equ 2 ; n has the value of 2 lp_cnt set x1 ; assign file register x1 to lp_cnt movlw n movwf lp_cnt, A ; prepare to repeat the loop for n times loop ; program loop ; decfsz lp_cnt,f,a ; decrement lp_cnt and skip if equal to goto loop ; executed if lp_cnt If the loop label is within 128 words from the branch point, use bra loop; otherwise use goto loop ) Program Development 4.9.1) Program 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 data ) Algorithm Representation Step 1 Step 2 Step ) Assembly program template org x ; program starting address after power on reset goto start org retfie org retfie (Before Interrupt is covered) x8 x18 ; high-priority interrupt service routine ; low-priority interrupt service routine start ; your program is here! end 81 Lecturer: Dr Jamaludin Bin Omar 4-14

15 4.9.4) Case issues The PIC18 instructions can be written in either uppercase or lowercase. MPASM allows the user to include p18fxxxx.inc file to provide register definitions for the specific processor. All special function registers and bits are defined in uppercase. The convention followed in the textbook is: using lowercase for instructions and directives, using uppercase for special function registers. 82 Two conventions for ordering the bytes within a word: Big Endian: the most significant byte of a variable is stored at the lowest address. Little Endian: the least significant byte of a variable is stored at the lowest address. Example: Double word in memory Little MPLAB 4.9.5) Byte order issues Big MPLAB for PIC18 is using Little Endian ) Programs for Arithmetic Computations 4.1.1) Perform Addition Operations 4.1.1) Perform Addition Operations (Cont) The program that implements Example 2.4 is as follows: Example 2.4: [Huang pg 57] Write a program that adds the three numbers stored in data registers at x2, x3, and x4 and places the sum in data register at x5. Pseudo Algorithm: Step 1 - Load the number stored at x2 into the WREG register. Step 2 - Add the number stored at x3 and the number in the WREG register and leave the sum in the WREG register. Step 3 - Add the number stored at x4 and the number in the WREG register and leave the sum in the WREG register. Step 4 - Store contents of the WREG register in the memory location at x5. 84 #include <p18f872.inc> ; can be other processor org x goto start org x8 retfie org x18 retfie start movf x2,w,a ; WREG [x2] addwf x3,w,a ; WREG [x2] + [x3] addwf x4,w,a ; WREG [x2] + [x3] + [x4] movwf x5,a ; x5 sum (in WREG) end 85 Lecturer: Dr Jamaludin Bin Omar 4-