Computer Architecture

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偿蛮沈
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1 ECE 3120 Computer Systems Assembly Programming Manjeera Jeedigunta Tel: , Prescott Hall 120

2 Prev: Basic computer concepts 68HCS12 addressing modes,instructions Today: Programming Structure Assembler Directives

3 3 Sections of a HCS12 Assembly Program Assembler directives Defines data and symbol Reserves and initializes memory locations Specifies output format Specifies the end of a program Assembly language instructions HCS12/MC9S12 instructions Comments Explains the function of a single or a group of instructions

4 Fields of a HCS12 Instruction label: opcode Instruction Label field Optional Starts with a letter and followed by letters, digits, or special symbols (_ or.) Can start from any column if ended with : Must start from column 1 if not ended with : Operation field Contains the mnemonic of a machine instruction or an assembler directive Separated from the label by at least one space operands ;comments Operand field Follows the operation field and is separated from the operation field by at least one space Contains operands for instructions or arguments for assembler directives Comment field Any line starts with an * or ; is a comment Separated from the operand and operation field for at least one space Optional

5 Identify the Four Fields of an Instruction loop ADDA #$40 ; add 40 to accumulator A (1) loop is a label (2) ADDA is an instruction mnemonic (3) #$40 is the operand (4) add #$40 to accumulator A is a comment movb 0,X,0,Y ; memory to memory copy (1) no label field (2) movb is an instruction mnemonic (3) 0,X,0,Y is the operand field (4) ; memory to memory copy is a comment

6 Assembler Directives END Ends a program to be processed by an assembler Any statement following the END directive is ignored. ORG The assembler uses a location counter to keep track of the memory location where the next machine code byte should be placed. This directive sets a new value for the location counter of the assembler. The sequence ORG $1000 LDAB #$FF places the opcode byte for the instruction LDAB #$FF at location $1000.

7 dc.b (define constant byte) db (define byte) fcb (form constant byte) - These three directives define the value of a byte or bytes that will be placed at a given location. - These directives are often preceded by the org directive. - For example, org $800 array dc.b $11,$22,$33,$44 dc.w (define constant word) dw (define word) fdb (form double bytes) - Define the value of a word or words that will be placed at a given location. - The value can be specified by an expression. - For example, vec_tab dc.w $1234, abc-20

8 fcc (form constant character) Used to define a string of characters (a message) The first character (and the last character) is used as the delimiter. The last character must be the same as the first character. The delimiter must not appear in the string. The space character cannot be used as the delimiter. Each character is represented by its ASCII code. Example msg fcc Please enter 1, 2 or 3:

9 fill (fill memory) - This directive allows the user to fill a certain number of memory locations with a given value. - The syntax is fill value,count - Example space_line fill $20,40 ds (define storage) rmb (reserve memory byte) ds.b (define storage bytes) - Each of these directives reserves a number of bytes given as the arguments to the directive. - Example buffer ds 100 reserves 100 bytes

10 Storage ds.w (define storage word) rmw (reserve memory word) - Each of these directives increments the location counter by the value indicated in the number-of-words argument multiplied by two. - Example dbuf ds.w 20 reserves 40 bytes starting from the current location counter equ (equate) - This directive assigns a value to a label. - Using this directive makes one s program more readable. - Examples arr_cnt equ 100 oc_cnt equ 50

11 loc This directive increments and produces an internal counter used in conjunction with the backward tick mark (`). -No need to think up new labels: loc loc ldaa #2 same as ldaa #2 loop` deca loop001 deca bne loop` bne loop001 loc loc loop` brclr 0,x,$55,loop` loop002 brclr 0,x,$55,loop002

12 Macro A name assigned to a group of instructions - Use macro and endm to define a macro - Example of macro sumof3 macro arg1,arg2,arg3 ldaa arg1 adda arg2 adda arg3 endm - Invoke a defined macro: write down the name and the arguments of the macro is replaced by sumof3 $1000,$1001,$1002 ldaa $1000 adda $1001 adda $1002

13 Next Software Development Issues Programming Arithmetic

第 15 章程式編写語言 15.1 程式編写語言的角色程式編寫語言是程式編寫員與電腦溝通的界面語法是一組規則讓程式編寫員將字詞集合起來電腦是處理位元和字節的機器, 與

第 15 章程式編写語言 15.1 程式編写語言的角色程式編寫語言是程式編寫員與電腦溝通的界面語法是一組規則讓程式編寫員將字詞集合起來電腦是處理位元和字節的機器, 與程式編写語言在完成這章後, 你將能夠了解程式編写語言的功能了解高階語言和低階語言之間的分別知道翻譯程式的意義和能夠把翻譯程式分類為 : 匯編程式編譯程式和解譯程式認識不同翻譯程式的優點和缺點程式是指揮電腦的指