Chapter 1 Introduction to HCS12/MC9S12

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Chapter 1Introduction to HCS12/MC9S12
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What is a Computer?

• Software
• Hardware

Computer Hardware Organization
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The Processor

• Registers
• Storage locations in the processor
• Arithmetic logic unit
• Control unit
• Program counter keeps track of the address of the
  next instruction to be executed.
• Status register flags the instruction execution
  result.
• The microprocessor
• A processor implemented on a very large scale
  integration (VLSI) chip
• Peripheral chips are needed to construct a
  product
• The microcontroller
• The processor and peripheral functions
  implemented on one VLSI chip

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Features of the HCS12 Microcontroller

• 16-bit CPU
• 64 KB memory space (also supports expanded memory
  up to 1 MB through a 16-KB window)
• 0 KB to 4KB of EEPROM
• 2 KB to 14 KB of on-chip SRAM
• 32 KB to 512 KB flash memory
• Sophisticated timer functions that include input
  capture, output compare, pulse accumulators,
  real-time interrupt, and COP timer
• Serial communication interfaces SCI, SPI, CAN,
  BDLC
• Background debug mode (BDM)
• 10-bit A/D converter
• Instructions for supporting fuzzy logic function

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Semiconductor Memory (1 of 2)

• Random-access memory (RAM) same amount of time
  is required to access any location on the same
  chip
• Dynamic random-access memory (DRAM) periodic
  refresh is required to maintain the contents of a
  DRAM chip
• Static random-access memory (SRAM) no periodic
  refresh is required
• Read-only memory (ROM) can only be read but not
  written by the processor
• Mask-programmed read-only memory (MROM)
  programmed when being manufactured
• Programmable read-only memory (PROM) is
  fuse-based, can be programmed by the end user by
  a burner.

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Semiconductor Memory (2 of 2)

• Erasable programmable ROM (EPROM)
• Electrically programmable many times
• Erased by ultraviolet light (through a window)
• Erasable in bulk (whole chip in one erasure
  operation)
• Electrically erasable programmable ROM (EEPROM)
• Electrically programmable many times
• Electrically erasable many times
• Can be erased one location, one row, or whole
  chip in one operation
• Flash memory
• Electrically programmable many times
• Electrically erasable many times
• Can only be erased in bulk or a sector at a time

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Computer Software

• Computer programs are known as software.
• A program is a sequence of instructions.
• Machine instruction
• A sequence of binary digits which can be executed
  by the processor
• 0001 1000 0000 0110 A ? A B
• 0100 0011 A ? A 1
• 1000 0110 0000 0110 A ? 6
• Hard to understand, enter, debug, and maintain
  for human being

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Assembly Language

• Defined by assembly instructions
• An assembly instruction is a mnemonic
  representation of a machine instruction
• ABA A ? A B
• DECA A ? A 1
• Assembly programs must be translated into machine
  instructions before it can be executed --
  translated by an assembler
• There are two kinds of assemblers native
  assembler and cross assembler.
• Programmers need to work on the program logic at
  a very low level and cannot achieve high
  productivity.

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High-level Language

• Syntax of a high-level language is similar to
  English.
• A translator is required to translate the program
  written in a high-level language -- done by a
  compiler.
• There are two types of compilers native compiler
  and cross compiler.
• High-level languages allow the user to work on
  the program logic at higher level and achieve
  higher productivity.
• Source code
• A program written in assembly or high-level
  language
• Object code
• The output of an assembler or compiler

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machine code
source code
line
addr.
1 2 3 4 5 6
org 2000 ldaa 1000 adda 1001 adda 1002 staa 1
100 end
2000 2003 2006 2009
00002000 B6 1000 BB 1001 BB 1002 7A 1100
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Memory Addressing

• Memory consists of a sequence of directly
  addressable locations.
• A location is referred to as an information unit.
• A memory location can be used to store data,
  instruction, and the status of peripheral
  devices.
• A memory location has two components an address
  and its contents.

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• Data transfers between the CPU and the memory are
  done over the common buses address bus and data
  bus.
• Notations maddr represents the contents of a
  memory location, reg refers to the contents of
  a register.
• For example, 20 refers to the contents of
  memory location at 20.
• A refers to the contents of accumulator A.

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Addressing Modes

• A HCS12 instruction consists of one or two bytes
  of opcode and zero to five bytes of operand
  addressing information.
• Opcode bytes specify the operation to be
  performed by the CPU.
• The first byte of a two-byte opcode is always
  18.
• Addressing modes specify the operand to be
  operated on.
• The addressing mode may specify a value, a
  register, or a memory location to be used as an
  operand.

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Inherent Mode

• Instructions that use this mode do not use extra
  bytes to specify operands because the
  instructions either do not need operands or all
  operands are CPU registers.
• Operands are implied by the opcode.
• Examples
• NOP
• INX
• DECA

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Immediate Mode

• Operands for instructions that use immediate mode
  are included in the instruction.
• CPU does not access memory for operands.
• Example
• LDAA 55
• LDX 1000

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Direct Mode

• This mode can only specify memory locations in
  the range of 0 - 255.
• This mode uses only one byte to specify the
  operand address.
• Example
• LDAA 20
• LDAB 40

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Extended Mode

• In this mode, the full 16-bit address is provided
  in the instruction.
• For example,
• LDAA 4000
• LDX FE60

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Relative Mode (1 of 2)

• Used only by branch instructions
• Short and long conditional branch instructions
  use exclusively relative mode.
• BRCLR and BRSET instructions can also use
  relative mode to specify branch target.
• A short branch instructions consists of an 8-bit
  opcode and a signed 8-bit offset.
• The short relative mode can specify a range of
  -128 127.
• A long branch instruction consists of an 8-bit
  opcode and a signed 16-bit offset.
• The range of the long relative mode is from
  -32768 32767.
• A programmer uses a symbol to specify the branch
  target and the assembler will figure out the
  actual branch offset (distance) from the
  instruction that follows branch instruction.

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Relative Mode (2 of 2)

• For example,
• minus
• bmi minus

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Indexed Mode

• This mode uses the sum of an index register (X,
  Y, PC, or SP) and an offset to specify the
  address of an operand.
• The offset can be a 5-bit, 9-bit, and 16-bit
  signed value or the value in accumulator A, B, or
  D.
• Automatic pre- or post-increment or pre- or
  post-decrement by -8 to 8 are options.
• PC can be used as the index register for all but
  auto-increment or auto-decrement mode.
• Indirect indexing with 16-bit offset or
  accumulator D as the offset is supported.
• A summary of indexed addressing modes is given in
  Table 1.3.

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Indexed Addressing (1 of 2)

• 5-bit Constant Offset Indexed Addressing
• The base index register can be X, Y, SP, or PC.
• The range of the offset is from -16 to 15.
• Examples
• ldaa 0,X
• stab -8,0
• 9-bit Constant Offset Indexed Addressing
• The base index register can be X, Y, SP, or PC.
• The range of the offset is from -256 to 255.
• Examples
• ldaa FF,X
• ldab -20,Y

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Indexed Addressing (2 of 2)

• 16-bit Constant Offset Indexed Addressing
• The base index register can be X, Y, SP, or PC.
• This mode allows access any location in the 64-KB
  range.
• Examples
• ldaa 2000,X
• staa 4000,Y
• 16-bit Constant Indirect Indexed Addressing
• A 16-bit offset is added to the base index
  register to form the address of a memory location
  that contains a pointer to the memory location
  affected by the instruction.
• The square brackets distinguish this addressing
  mode from the 16-bit constant offset indexing.
• Example,
• ldaa 10,X
• staa 20,Y

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Auto Pre/Post Decrement/Increment Indexed
Addressing

• The base index register can be X, Y, or SP.
• The index register can be incremented or
  decremented by an integer value either before or
  after indexing taking place.
• The index register retains the changed value
  after indexing.
• The value to be incremented or decremented is in
  the ranges -8 thru -1 or 1 thru 8.
• The value needs to be related to the size of the
  operand or the current instruction.
• Examples
• staa 1,-SP
• staa 1,SP-
• ldx 2,SP
• ldx 2,SP

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Accumulator Offset Indexed Addressing

• The effective address of the operand is the sum
  of the accumulator and the base index register.
• The base register can be X, Y, SP, or PC.
• The accumulator can be the 8-bit A or B or the
  16-bit accumulator D.
• Example
• ldaa B,X
• stab B,Y

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Accumulator D Indirect Indexed Addressing
The value in D is added to the value in the base
index register to form the address of the memory
location that contains the address to the memory
location affected by the instruction. The square
brackets distinguish this addressing mode from
accumulator D offset indexing. Example jmp D,P
C go1 dc.w target1 go2 dc.w target2 go3 dc.w targ
et3 target1 . target2 . target3
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HCS12 Instruction Examples

• The LOAD and STORE instructions
• The LOAD instruction copies the contents of a
  memory location or places an immediate value into
  an accumulator or a CPU register.
• STORE instructions save the contents of a CPU
  register into a memory location.
• N and Z flags of the CCR register are
  automatically updated and the V flag is cleared.
• All except for the relative mode can be used to
  select the memory location or value to be loaded
  into an accumulator or CPU register.
• All except for the relative and immediate modes
  can be used to select memory location to store
  contents of the CPU register. For example,
• ldaa 0,X
• staa 20
• stx 8000
• ldd 100

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Transfer and Exchange Instructions (1 of 2)

• Transfer instructions copy the contents of a CPU
  register or accumulator into another CPU register
  or accumulator.
• TFR is the universal transfer instruction, but
  other mnemonics are accepted for compatibility
  with the 68HC11.
• The TAB and TBA instructions affect the N, Z, and
  V condition code bits.
• The TFR instruction does not affect any condition
  code bits. For example,
• TFR D,X D ? X
• TFR A,B A ? B
• TFR A,X 0A ? X upper 8-bit of X is
  cleared to 0
• TFR X,A X70 ? A lower 8 bits copied to A

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Transfer and Exchange Instructions (2 of 2)

• The EXG instruction exchanges the contents of
  a pair of registers or accumulators. For example,
• exg A, B
• exg D,X
• exg A,X A ? X70, X ? 00A
• exg X,B X ? 00B, B ? X70
• The SEX instruction sign-extend an 8-bit twos
  complement number into a 16-bit number so that it
  can be used in 16-bit signed operations. For
  example,
• SEX A,X

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Move Instructions

• These instructions move data bytes or words from
  a source to a destination in memory.
• Six combinations of immediate, extended, and
  index addressing modes are allowed to specify the
  source and destination addresses
• IMM ? EXT, IMM ? IDX, EXT ? EXT, EXT ?
  IDX, IDX ? EXT, IDX ? IDX
• For example,
• movb 100,800
• movw 0,X, 0,Y

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Add and Subtract Instructions

• These instructions perform fundamental arithmetic
  operations.
• The destinations of these instructions are always
  a CPU register or accumulator.
• There are two-operand and three-operand versions
  of these instructions.
• Three-operand ADD or SUB instructions always
  include the C flag as one of the operand.
• Three-operand ADD or SUB instructions are used to
  perform multi-precision addition or subtraction.
• Example
• adda 1000 A ? A 1000
• adca 1000 A ? A 1000 C
• suba 1002 A ? A 1002
• sbca 1000 A ? A - 1000 - C

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• Instruction Execution Cycle
• One or more read cycles to fetch instruction
  opcode bytes and addressing information
• One or more read cycles to fetch the memory
  operand (s) (optional)
• Perform the operation specified by the opcode
• One or more write cycles to write back the result
  to either a register or a memory location
  (optional)
• Instruction Queue
• The HCS12 executes one instruction at a time and
  many instructions take several clock cycles to
  complete.
• When the CPU is performing the operation, it does
  not need to access memory.
• The HCS12 prefetches instructions when the CPU is
  not accessing memory to speedup the instruction
  execution process.
• There are two 16-bit queue stages and one 16-bit
  buffer. Unless buffering is required, program
  information is first queued in stage 1, and then
  advanced to stage 2 for execution.

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Embedded System Any product that uses a
microprocessor or microcontroller as its
controller. Functionality is the focus not the
processor itself. Weather Station
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Other Examples of Embedded System

• Cell phone making the phone call, accepting
  incoming call, accessing Internet, displaying
• Web page handling input/output, keeping track of
  time, taking picture, and playing game
• Home security system sensing external
  temperature, smoke, humidity, and intruders
  taking appropriate actions according to the
  detected events
• Automobile monitoring speed, gas level,
  temperature, distance, direction, and so on
  controlling display, full injection, air bag
  deployment, cruising, and so on giving warnings
• Network router responsible for message routing,
  congestion and traffic control, and so on