Assembly Language ELEC 330 Digital Systems Engineering Dr. Ron Hayne

330_032 The Assembly Process  Assembly Language Symbolic representation of instructions and data Source module (.ASM)  Assembler Program which translates symbols to machine code Object/Load module (.S19) Listing (.LST)  Loader Utility that places machine code into target memory Some assemblers require Linker to convert object module into load module

330_033 Source & Load Modules  Source Module (.ASM) Symbolic Instructions, Data and Addresses Instruction mnemonics Symbols Assembler Directives Control instructions for assembler program Comments Explanation of program  Load Module (.S19) Binary Instructions and Data Object Module Load Information Address information Error-checking info Checksum

330_034 Listing (.LST)  Source Code Source Module  Object Code Object Module  Symbol Table User symbols Numeric values of symbols (Cross-references)  Error Messages

330_035 Motorola Assembly Language  Source Statement Single line of program Symbols and Numbers  Spaces (or tabs) delineate fields Label Operation Operand Comment Line beginning with an * is also a comment

330_036 Numbers and Symbols  Numbers Assembler translates into 16-bit binary  Number Systems Decimal 34, -34 Hex $12, $ABCD Binary %1001, %  Symbols Characters used to represent addresses or data Assembler translates into numbers Characteristics One to six alphanumeric characters First character a letter Can’t be single letter A, B, X, or Y Must be unique

330_037 Addressing Modes Addressing Mode Operand Format Operand Type Example Inherentnone INCA Immediate#operanddata numberLDAB #40 ExtendedoperandaddressSTAA LENGTH DirectoperandaddressSUBA COUNT Indexedoperand,XoffsetLDD 0,X Relativeoperandaddress/offsetBVS LOOP

330_038 Assembler Directives  ORGorigin  RMBreserve memory bytes  FCBform constant bytes  FCCform constant characters  FDBform double-bytes  EQUequate  ENDend

330_039 Source Module (.ASM) * This line is a comment * CONSTEQU17 * ** Data Section ORG$20 DATA1FCB$10 DATA2FDB$B610 STORERMB3 VALUEFCB20 ORG$B600 PTRNFCB% SAVERMB1 *

330_0310 Source Module (.ASM) ** Program Section ORG$E100 STARTLDAAVALUE DECA STAASAVE LDAB#23 LDXDATA2 STABCONST,X DONEBRADONE "STOP" * ORG$FFFEreset vector FDBSTARTset to start END

330_0311 Assembler Listing (.LST) * This line is a comment * CONST EQU 17 * ** Data Section ORG $ DATA1 FCB $ B6 10 DATA2 FDB $B610 STORE RMB VALUE FCB 20 ORG $B600 B600 0C PTRN FCB % SAVE RMB 1 *

330_0312 Assembler Listing (.LST) ** Program Section ORG $E100 E START LDAA VALUE E102 4A DECA E103 B7 B6 01 STAA SAVE E106 C6 17 LDAB #23 E108 DE 21 LDX DATA2 E10A E7 11 STAB CONST,X E10C 20 FE DONE BRA DONE "STOP" * ORG $FFFE reset vector FFFE E1 00 FDB START set to start END

330_0313 Assembler Listing (.LST) Symbol Table CONST 0011 DATA DATA DONE E10C PTRN B600 SAVE B601 START E100 STORE 0023 VALUE 0026

330_0314 THRSim11  68HC11 Simulator setup setup license  Source Module (.ASM) Assemble Object/Load Module (.S19) Listing (.LST) Label Window (List) Memory List  Memory Map $0000-$00FFRAM $1000-$103FI/O $B600-$B7FFRAM $E000-$FFFFROM  Run (Step) CPU Registers Memory List  Reset

330_0316 Project 1  THRSim11 Write, Assemble, Test Copy-a-table Program (Figure 2-49, p.108)  Individual Work  Due Date See web site

330_0317 Bad Assembly Language  Bad Documentation too little, too much confusing comments  Bad Labels confusing meaningless  Bad Numbers mixed bases complex calculations  Bad Expressions single/double-bytes mixed constants  Bad Instructions mixed addresses/data  Extraneous Statements unused symbols unused instructions

330_0318 * Bad Example * CONST EQU $15 * ORG 32 Data Section MARY FCB $ BOB FDB $ABCD/ ABCDEF FCB CONST+BOB LDAA RMB A A FCB $A 0026 EC TWOONES FCB % START LDAA LDAA A DEC A 002C STAA $45 Load the A reg 002E C6 20 LDAB #MARY 0030 D7 25 STAB ABCDEF DF 15 STX CONST 0034 E7 20 STAB MARY,X F3 BRA START F SWI "Stop" END

330_0319 Summary  Assembly Process Source Module (.ASM) Object/Load Module (.S19) Listing (.LST)  Assembly Language Label, Operation, Operand, Comment Numbers, Symbols Addressing Modes  Assembler Directives  THRSim11