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Chapter 6

Chapter 6. Introduction to Data Structures. Defining Constant. <Label> EQU <value> XVAL EQU 7 MOVE.B #XVAL, D0. Defining Variables with DC and DS. For temporary storage of value Why we do not store it is registers? Address & data registers are limited to 16 Initialize the memory

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Chapter 6

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  1. Chapter 6 Introduction to Data Structures

  2. Defining Constant • <Label> EQU <value> • XVAL EQU 7 • MOVE.B #XVAL, D0

  3. Defining Variables with DC and DS • For temporary storage of value • Why we do not store it is registers? • Address & data registers are limited to 16 • Initialize the memory • DC – Define Constant • DS – Define Storage • <label> DC.size <value> • This is particularly useful when we initialize an array of data or collection of identical data types. • MNO DC.B 1, 2, 3, 4 • STU DC.B ‘Hello!’ • When we want to reserve the space for the variable without initializing them then we use DS directive

  4. Question • How many bytes in total is reserved by the three statements below. • SVAL DS.B 6 • TVAL DS.W 2 • UVAL DS.BL 3

  5. Accessing one Dimensional Array • MOVE.B (A0, D7), D0// read • MOVE.B D0, (A0, D7)// write

  6. Designing Modules • Always design smaller modules for handeling your program. • Some of the popular module may be • Initialize • Getword • Lookup • Insert • Makecount • Increase

  7. Loops • If-Else Loop • BSR Lookup • CMPI.B #0, D5 • BEQ ThenCode • Code for else • Repeat-Until Loop • MOVE.B #100, D2 • AGAIN BSR GETDATA • BSR ProcessData • SUBI.B #1, D2 • BNE AGAIN

  8. LOOPS • Do-While Loop • WHILE CMPI.B #’A’, D1 • BEQ NEXT • <other loop instructions> • BRA WHILE • NEXT ---- • CASE Statement • CMPI.B #0, D1 • BNE C1 • CLR.B D2 • BRA Next • C1 CMPI.B #1, D1 • BNE C2 • ADDI.B #1, D2 • BRA Next • C2 CMPI.B #2, D2 • BNE Next • SUBI.B #1, D2 • Next ----

  9. Accessing 1-D Arrays • EA : Effective Address • Base: Base Address, The starting address of the array • Index: Element Size • Offset: Offset into array to element’s position • EA = Base + Offset • Offset = Size * Index • Example: The starting address of a word array is 830C, What is the address of the word whose index value is 5

  10. Accessing 2-D Arrays • It is like a matrix containing row and column • We can store the values using the keyword DC • Example: • Sub DC.B 6, 1, 8 • DC.B 7, 5, 3 • DC.B 2, 9, 4 • Val = sub [row] [column] • Col: Column Number • Row Offset: Offset into matrix to element’s row • Column Offset: Offset into row to element’s position • EA = Base + Rowoffset + ColumnOffset • RowOffset = Row * Size * NCols • ColumnOffset = Size * Col

  11. Searching an Item from the DataBase • ORG $8000 • DATA DS.B 100 • ITEM DS.B 1 • ORG $8100 • FINDBYTE MOVEA.L #DATA, A0 • MOVE.W #99, D0 • MOVE.B ITEM, D1 • COMPARE CMP.B (A0)+, D1 • BEQ FOUND • DBRA D0, COMPARE • ANDI #$FE, CCR • RTS • FOUND ORI #$01, CCR • RTS

  12. STACK • Push CMPA.L A0,A1 • BEQ STKFULL • MOVE.L D0, -(A0) • CLR.B D1 • RTS • STKFULL MOVE.B #$80, D1 • RTS • CMPA.L A0, A2 • BEQ STKEMPTY • MOVE.L (A0)+, D0 • CLR.B D1 • RTS • STKEMPTY MOVE.L #$FF, D1 • RTS

  13. QUEUE • A0: Pointer to write operation • A1: Pointer to read operation • A2: Contains the end of queue Address • A3: Contains the beginning of queue Address • INQUEQE CMPA.L A0, A2 • BNE NO • MOVEA.L A3, A0 • NO MOVE.L D0, (A0) • SUBA.L #4, A0 • RTS • OUTQUEUE CMPA.L A1, A2 • BNE NO1 • MOVEA.L A3, A1 • NO1 MOVE.L (A1), D0 • SUBA.L #4, A1 • RTS

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