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ME4447/6405

ME4447/6405. Microprocessor Control of Manufacturing Systems and Introduction to Mechatronics Instructor: Professor Charles Ume Lecture #9. Assembly Language. Reading assignments for this week and next week Read Chapters 5-8 in Basic Microprocessors and the 6800, by Ron Bishop.

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ME4447/6405

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  1. ME4447/6405 Microprocessor Control of Manufacturing Systems and Introduction to Mechatronics Instructor: Professor Charles Ume Lecture #9

  2. Assembly Language

  3. Reading assignments for this week and next week Read Chapters 5-8 in Basic Microprocessors and the 6800, by Ron Bishop. Chapter 5 Microcomputers-What Are They? Chapter 6 Programming Concepts Chapter 7 Addressing Modes Chapter 8 M6800 Software There will be questions and answers the rest of this week and next week based on your reading assignment. Reading Assignments

  4. HC12S CPU can only understand instructions written in binary called Machine Language. Writing programs in Machine Language is extremely difficult Mnemonics are simple codes, usually alphabetic, that is representative of instruction it represents (example: LDAA [LoaDAccumulator A]) A program written using Mnemonic Instructions is called Assembly Language program An Assembler can be used to translate Assembly Language program to Machine Language Program, and put it in S-Record Format. Why use Assembly Language?

  5. Address: Common term for memory location. Always written in hexadecimal. $4000 is the 4000th16 Memory Location (Note: “$” signifies hexadecimal) Literal Value: A number used as data in program indicated by “#”. Can be represented in the following ways: #$FF = hexadecimal number FF #%1011 = binary number 1011 (Note: “%” signifies binary) #123 = decimal number 123 A Literal Value can be stored in an address Example: Literal Value #$FF can be stored in address $4000 Example 2: Literal Value #$FE0A is stored in address $2000 (Note: #$FE is stored in address $2000 #$0A is stored in address $2001) Assembly Language Notations

  6. Directives: Instructions from the programmer to Assembler NOT to microcontroller Example 1: ORG <address> Store translated machine language instructions in sequence starting at given address for any mnemonic instructions that follow Example 2: END Stop translating mnemonics instructions until another ORG is encountered (Note: More will be covered in later lectures) Assembly Language Directives

  7. Assembly Language Format (Note: Last three options are called Operands) Data that the Assembly Directive uses Or Blank if Mnemonic Instruction does not need Data Or Offset Address used to modify Program Counter by a Mnemonic Instruction Or Data that Mnemonic Instruction uses Or Address where the Data that Mnemonic Instruction will use is stored A Tab (8 white spaces) or Label (Note: A Label is another Assembly Directive and will be covered in later lectures) Assembly Directive Or Mnemonic Instruction Left margin of assembly program

  8. ORG $0800 LDAA #$100A - - BNE Front 27 0E LDAB $2F,Y STAB $110C - - Front INCX - - SWI END

  9. In the previous slide, there were several options for the operand: Blank if Mnemonic Instruction does not need Data Offset Address used to modify Program Counter by a Mnemonic Instruction Data that Mnemonic instruction uses Address were Data that Mnemonic instruction uses is stored Which option a programmer uses is defined by the following addressing modes: Addressing Modes • Inherent • Immediate • Extended • Indexed Indirect • Direct • Indexed • Relative (Note: All instructions are not capable of all addressing modes. Example: BLE [Branch if Less than or Equal to Zero] is only capable of Relative addressing mode)

  10. Example: Programming Reference Guide Page 6

  11. Example: Write a program to clear accumulator A. Start programming at address $1000 Solution: ORG $1000 CLRA SWI END CLRA [ CLeaR accumulator A] is an instruction using Inherent Addressing (NOTE: SWI [SoftWare Interrupt] is a mnemonic instruction which tells the 9SC32 to store the content of cpu registers on the stack. Sets the I bit (the interrupt bit) on the CCR. Loads the program counter with the address stored in the SWI interrupt vector, and resume program execution at this location. If no address is stored in the SWI vector, the main program will stop execution at this point. Used in this course to return control to Mon12 Program) Blank if Mnemonic Instruction does not need Data If Mnemonic Instruction does not need data then it uses Inherent Addressing Mode

  12. Example: Write a program to load accumulator A with #$12. Start programming at address $1000 Solution: ORG $1000 LDAA #$12 SWI END LDAA is an instruction using Immediate Addressing mode in this example Data that Mnemonic instruction uses The Mnemonic instruction is using Immediate Addressing mode if the operand is Data used by the instruction

  13. Address were Data that Mnemonic instruction uses is stored The following addressing modes apply if the operand is an Address containing Data used by Mnemonic instruction : • Direct • Data is contained in Memory locations $00 to $FF • Address is given as a single byte address between $00 to $FF • Instructions using Direct addressing has fastest access to memory • Example: LDAA $00 • Loads accumulator A with Data value stored at memory location $00 • Extended • Data is contained in Memory locations $0100 to $FFFF • Address is given as a two byte address between $0100 to $FFFF • Example: LDAA $2000 • Loads accumulator A with Data value stored at memory location $2000

  14. Example : Write a program to add the numbers 1010 and 1110. Solution ORG $1000 LDAA #$0A *Puts number $0A in acc. A LDAB #$0B *Puts number $0B in acc. B ABA *Adds acc. B to acc. A STAA $00 *Stores results in address $00 SWI *Software interrupt END LDAB and LDAA use immediate addressing mode STAA uses direct addressing mode Example Problem 1

  15. Address were Data that Mnemonic instruction uses is stored (Continued) • Indexed: • Data is located within Memory locations $00 to $FFFF • Example: Store content of $2003 in Register A • LDX #$2000 • LDAA $03,X • Loads accumulator A with Data value stored at memory location $2003 • X + $03 = $2000 + $03 = $2003 • (Note: LDX [ LoaD index register X])

  16. Why is Indexed Addressing Mode needed? Example: Store Data Value #$20 into memory locations $2000 to $3000 Without Indexed Addressing Mode With Indexed Addressing Mode • ORG $1000 • LDAA #$20 • LDX #$2000 • LOOP STAA $00,X • INX • CPX #$3001 • BNE LOOP • SWI • END ORG $1000 LDAA #$20 STAA $2000 STAA $2001 . . . STAA $3000 SWI END Program on the Left is much longer than program on Right

  17. ORG $1000 LDY #$1001 LDAA #$20 LDX #$2000 LOOP STAA $00,X INX DECY BNE LOOP SWI END Why is Indexed Addressing Mode needed? Example: Store Data Value #$20 into memory locations $2000 to $3000

  18. Why is Indexed Addressing Mode needed? (Continued) • ORG $1000 • LDAA #$20 • LDX #$2000 • LOOP STAA $00,X • INX • CPX #$3001 • BNE LOOP • SWI • END Note: LDX [ LoaD accumulator A] STAA [ STore Accumulator A] INX [ INcrement X] CPX [ ComPare X] BNE [Branch if Not Equal]( is using relative addressing in conjunction with label “LOOP”) LOOP, BNE LOOP, INX, and CPX #$3001 creates a loop. Loop1: Data in accumulator A (#$20) is stored at $2000 + $00 Data in X is incremented #$2000 + #$0001 = #$2001 Data in X is compared to #$3001 Not equal so do another loop Loop2: Data in Accumulator A (#$20) is stored at $2001 Data in X is incremented #$2001 + #$0001 = #$2002 Data in X is compared to #$3001 Not equal so do another loop Etc…..

  19. Types of Indexed modes of Addressing • Indexed addressing may be implemented in multiple ways. HCS12 CPU uses X, Y, SP or PC as base index registerfor instruction. Offset is then added to base index register to form effective address. • Constant offset 5-, 9- or 16-bit signed offset (-16 to +15, -256 to +255, -32768 to +32767) 5-Bit Constant Offset Indexed Addressing Index mode uses 5-bit signed offset which is added to base index register (X, Y, SP or PC) to form effective address of memory location that will be affected by instruction. Offset ranges from -16 through +15. Majority of indexed instructions in real programming use offsets that fit in shortest 5-bit form of indexed addressing. Contents of base registers remain unchanged. • LDAA $00, X *load A with (X + $00) The following three statements are equivalent: • STAA -8,X Note: offset given in decimal • STAA -$08,X Note: offset given in hex • STAA $FFF8,X Note: offset given as 16-bit number • Let X contain #$3000. After program executed, content of A will be stored at address (#$3000 - #$08) = $2FF8

  20. Types of Indexed modes of Addressing • 9-Bit Constant Offset Indexed Addressing. • Uses 9-bit signed offset which is added to base index register (X, Y, SP or PC) to form effective address of memory location affected by instruction. Offset ranges from -256 through +255. Contents of base registers are not changed after instruction is executed. MSB (sign bit) of offset is included in instruction postbyte and remaining 8 bits are provided as extension byte after instruction postbyte in instruction flow. • LDAA $FF, X *Assume X contains $1000 prior to instruct. Execut. • A6 E0 FF • LDAB -20, Y *Assume Y contains $2000 prior to instruct. Execut. • E6 E9 EC • First instruction will load A with value from ($1000 + $FF) = $10FF • Second instruction will load B with value from ($2000 – 20) = $IFEC

  21. Accumulator Offset Indexed Addressing In this indexed addressing mode, effective address is sum of values in base index register and unsigned offset in one of accumulator. Value in base index register is not changed. Indexed register can be X, Y, SP or PC and accumulator can be either 8-bit (A or B) or 16-bit (D) A, B, or D accumulator added to base index register to form address Content of accumulator is unsignedoffset LDAA B, X Instruction adds B to X to form address from which A will be loaded. B and X are not changed by this instruction. Types of Indexed modes of Addressing

  22. Types of Indexed modes of Addressing - Continued • Auto Pre-/Post-Increment/Decrement • Base index register may be automatically incremented/decremented before or after instruction (Program Counter may not be used as base register) • No offset is available • May be incremented/decremented 1 to 8 times • Post-Increment (in ranges from 1 through 8): • LDX 2,SP+ *Index register X is loaded with contents of (Same as PULX) memory location in stack pointer, then stack pointer is incremented twice • Pre-Increment (in ranges from 1 through 8): • LDX 2,+SP *Stack pointer is incremented twice, • then Index register X is loaded with contents of memory location in stack pointer • Pre-Decrement (in ranges from -8 through -1): • STAA 1,-X *Index register X is decremented, then Accumulator A is stored in memory location stored in Index Register X

  23. Indexed Addressing Mode Postbyte Encoding (xb)

  24. Indexed Addressing Mode Postbyte Encoding (xb) - Continued

  25. Why is Pre-/Post-Increment/Decrement Useful? Example: Store Data Value #$20 into memory locations $2000 to $3000 Without Post-Increment With Post-Increment • ORG $1000 • LDAA #$20 • LDX #$2000 • LOOP STAA 1,X+ • CPX #$3001 • BNE LOOP • SWI • END • ORG $1000 • LDAA #$20 • LDX #$2000 • LOOP STAA $00,X • INX • CPX #$3001 • BNE LOOP • SWI • END Note: “1” refers to the number of post increments, not an offset! Program on the Left requires 1 more byte of program memory and takes 1 more cycle to execute per run through the loop than the program on the right. This may make a large difference when the program is large and complex or when dealing with values larger than 16-bits.

  26. Types of Indexed modes of Addressing - Continued • Indexed-Indirect [Differ Discussion of this for Now] • Like other indexed addressing modes, offset and base index register are added to form an effective address • Offset is either Accumulator D or a 16 bit constant offset • However, effective address is understood to contain address of memory location containing address to be acted upon. • Example: Clear the contents of the memory location pointed to by a pointer located in memory location $2000 • ORG $2000 • PTR RMB 2 *Note: The user places the address of the memory location to be cleared here • ORG $1000 • LDX $2000 • CLR [$00,X] • SWI • END • (Note: CLR [CLeaR Memory Location]) • Useful for efficiently forming switch case statements and other program flow operations in high level programming languages

  27. Example: Hex number is stored in $2000 LDD #$2000 *Loads accumulator D with #$2000 STD $100A *Stores content of Register D in Addresses $100A and $100B LDX #$1000 *Loads Register X with #$1000 LDAA [10,X] *#$0A is added to #$1000 in X-Register to form $100A. Next, CPU *goes to memory (address) locations $100A and $100B and fetch *address pointer $2000. Value stored in address $2000 is read and *loaded into accumulator A. Types of Indexed modes of Addressing - Continued

  28. Assembler

  29. As stated before the Assembler translates an assembly language program into a machine language program Format of machine language program Instruction Operand Or Blank if instruction does not use Operands Address where instruction is located Opcode Postbyte (Note: This format is for Lecture and Tests only !! The real format the assembler outputs is “S19” and will be shown to you in Lab)

  30. Postbyte and Opcode Reference All Mnemonics and associated Op-codes can be found in Programming Reference Guide pages 6-19 Example: Programming Reference Guide Page 12 (Note: LDAA outlined in red)

  31. Indexed Addressing Mode Postbyte Encoding (xb)

  32. Indexed Addressing Mode Postbyte Encoding (xb) - Continued

  33. Postbyte allows an op-code to be used for more than one instruction. Determined from Tables 1, 3 or 4 in the programming reference guide Postbyte Table 1 (Excerpt)

  34. (Programming Reference Guide)

  35. ORG $1000 LDAA #$0A LDAB #$0B ABA STAA $00 SWI END Hand Assembling Example: Assemble the following Program Operand Opcode Postbyte Address 86 0A $1000 C6 0B $1002 $1004 18 06 5A 00 $1006 $1008 3F (Note: $1002 since $86 is now at $1000 and $0A is at $1001)

  36. ORG $1000 LDAB #$0A *Load acc. B with number 0A STAB $1100 *Store acc. B in address $1100 INCB *Increment acc. B by 1 ADDB $1100 *Add memory location $1100 *to acc. B STAB $1090 *Store acc. B in address $1090 SWI *Software interrupt END Example Problem 1 (revisited)

  37. ORG $1000 LDAB #$0A STAB $1100 INCB ADDB $1100 STAB $1090 SWI END 1000 86 0A 1002 7B 1100 1005 52 1006 FB 1100 1009 7B 1090 100B 3F Hand Assemble Example Problem 1 (Revisited) Operand Opcode Postbyte Address

  38. Write a short assembly language program that stores the content of Port T in memory location $3000 after waiting for 0.05 seconds for the input data. Solution Recall: One machine cycle = 0.125 x 10-6 s (8 MHz Bus Clock) We want the HCS12 to wait 0.05 s/0.125 x 10-6 s = 400,000 cycles One good way to make the HCS12 wait is to create a loop. Example Problem 2

  39. LDY #$AD9C 2 cycles LDD #$0000 2 cycles LOOP ABA 2 cycles CPX $2000 3 cycles DEY 1 cycle BNE LOOP 3 cycles Assume the number of loops needed to wait is 2 bytes (2 + 3 + 1 + 3)*X + 4 = 400,000 cycles X = 44,44410 = $AD9C Wait Loop Note: These instructions are included to increase the operation time

  40. Solution *Remember that Port T is input upon reset ORG $1000 LDY #$AD9C *Load Y with 44,44410 LDD #$0000 *Clear Accumulator D LOOP ABA *Add the contents of B to A CPX $2000 *Compare X with the contents of *$2000 DEY *Decrement Y BNE LOOP *Branch to LOOP if Y is not equal *to zero LDAB $0240 *Load acc. B with content of $0240 STAB $3000 *Store content of acc. B in $3000 SWI *Software Interrupt END Example 2 Solution

  41. Homework 1 Write an assembly language program to clear the internal RAM in the MC9S12C32. Write a program to add even/odd numbers located in addresses $0800 through $0900. Homework 2 Write a program to find the largest signed number in a list of numbers stored in address $0A00 through $0BFF. Repeat for an unsigned number. Homework

  42. QUESTIONS???

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