Physics 413 Chapter 1: Introduction to the HCS 12 Microcontroller

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Physics 413Chapter 1 Introduction to the HCS 12
Microcontroller
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Computer Architecture

• What is a Digital Computer ? A computer is
  essentially a fast electronic calculating
  machine.
• What is a program ? A program is a set of very
  simple instructions that a computer can
  understand. Examples of simple instructions are
  ADD two numbers, Is X gt Y?, COPY A into the
  memory.
• What is Machine Language ? The set of
  exceedingly simple and primitive instructions
  that a computer can understand is called the
  Instruction Set or Machine Language.

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Architecture and Organization

• Computer Architecture deals with the design of
  those components of a computer that are
  accessible to a programmer. For instance, the
  Motorola 6800 does not have a MUL instruction but
  the Pentium does.
• Computer Organization deals with the
  implementation of the architecture and may be
  transparent to the programmer. For instance,
  precisely how is MUL implemented in the hardware?

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Levels of Abstraction

• L5 High-level Language (C, Java)
• L4 Assembly Language
• L3 Operating System
• L2 Instruction Set Architecture (ISA)
• L1 Microarchitecture Level
• L0 Digital Logic Level
• Transistors

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A Brief History of Computers

• First Generation - Vacuum Tubes - 1945-1955 ENIAC
  (Electronic Numerical Integrator and Computer)
  had 18,000 Vacuum Tubes, 1500 relays and weighed
  30 tons
• Second Generation - Transistors - 1955-65 - PDP
  -8 (DEC)
• Third Generation - IC - 1965-80 - IBM 360
• Fourth Generation - VLSI - Intel and AMD
  Processors

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Moores Law

• The number of transistors on a chip doubles every
  18 months

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All about microprocessors and microcontrollers

• ROM is where the program that initializes the PC
  is stored.
• RAM access is fast
• ADDRESS BUS carries the address of RAM, ROM, and
  other peripherals
• HCS12 has 16 multiplexed address and data lines
• DATA BUS carries data back and forth between the
  microprocessor and RAM, ROM, and other
  peripherals.

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Memory

• Big Endian 4 bytes arranged as0123 (32-bit
  word)
• Little Endian 4 bytes arranged 3210 (32-bit
  word)
• DRAM Organization
• nxn matrix structure is popular for large memory
  sizes
• RAS - Row Address Strobe
• CAS - Column Address Strobe
• RAS - CAS strategy reduces the number of pins but
  slows down access because two addressing cycles
  are required
• SRAM Fast for cache

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ROM

• ROM
• PROM
• EPROM - UV erasable
• EEPROM - Electrically erasable byte at a time
• FLASH - electrical block erasable - digital film
  - more like RAM!

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HCS12 Data Sheet

• http//www.freescale.com/files/microcontrollers/do
  c/data_sheet/HCS12DFAMILYPP.pdf

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HCS12 Architecture
B
A
A B D
X
Y
SP
PC
CCR
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Straight-line Programming

• In Paris they simply stared when I spoke to them
• in French I never did succeed in making those
• idiots understand their own language
• Mark Twain , The Innocents Abroad, 1869

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My First Program

• CLRA Clears accumulator A ( A 0 )
• INC A This instruction does this A 1
  A
• SWI Stop (software interrupt)

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Op-codes

• Assembly Language Memory Location
  Op-codes
• CLRA 2000 87
• INCA 2001 42
• SWI 2002 3F

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My Second Program

• LDAA 12
• ADDA 15
• SWI

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Object Code . . . Program 2

• Assembly Language Memory Location
  Op-codes
• LDAA 12 2000 86
• 2001 12
• ADDA 15 2002 8B
• 2003 15
• SWI 2004 3F

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Addressing Modes

• Inherent (implied) Simplest with no operand.
  One-byte op-code. Examples INCA and CLRA
• Immediate Operand specified is immediate (no
  memory access).
• Examples LDAA 12 and ADDA 15

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Immediate and Direct Modes

• Immediate LDAA 12 Load the hex number
  12
• op-code 86 12
• Direct LDAA 12 Load from
  memory location 0012
• op-code 96 12

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My Third Program

• Assembly Language Memory Location
  Op-codes
• LDAA 04
• STAA 15
• LDAA 08 ? ?
• ADDA 15
• SWI

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My Third Program

• Assembly Language Memory Location
  Op-codes
• LDAA 04 2000 86 04
• STAA 15 2002 97 15
• LDAA 08 2004 86 08
• ADDA 15 2006 9B 15
• SWI 2008 3F

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Extended Addressing Mode

• The extended addressing mode becomes
  indispensable when memory locations beyond the
  zero page must be addressed. This is the case
  for the HCS12 on the Dragon12 Board in the lab
• Here, as always, an example is worth a thousand
  words
• LDAA 3C5E Load A from memory location 3C5E
• Op-codes B6 3C 5E

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Three Trick Questions

• What is the outcome of B6 00 2A ?
• What is the outcome of LDAA 3C5E ?
• What is the outcome of STAB 3C44 ?

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Trick Questions . . . Answered!

• What is the outcome of B6 00 2A ? Legal but not
  very smart.
• What is the outcome of LDAA 3C5E ? Not Legal
• What is the outcome of STAB 3C44 ? O.K. and
  op-code is F7 3C 44

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Index Register

• X is a 16-bit register
• How are the following three instructions
  different?
• LDX 5C42
• LDX 5C42
• LDX 5C

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Index Register

• LDX 5C42 The number 5C42 is loaded into X
• LDX 5C42 Numbers from 5C43 and 5C42 loaded
• LDX 5C Numbers from 005D and 005C
  loaded

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Indexed Addressing Mode

• LDAA 0,X loads accumulator A with the contents
  of the memory location pointed to by the index
  register X.
• LDAA 4,X loads accumulator A with the contents
  of the memory location pointed to by X4

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Transfer and Exchange!

• TFR D,X transfers the contents of D to X
• TFR X, B transfers bits 0-7 of X to B
• EXG A,B swaps A and B

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Move it!

• Memory to memory transfer
• movb 1000,2000 copies the (8-bit)contents of
  memory location 1000 to the memory location
  2000
• movw 0,X,0,Y copies the 16-bit word pointed to by
  X to the memory location pointed to by Y.

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Examples Galore

• ADDA The outcome is A M A
• ADDA 2B 8B 2B
• ADDA 3C 9B 3C
• ADDA 5B24 AB 5B 24

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Carry Bit in CCR

• ADCA The outcome is A M C A
• Use this instruction when expecting a carry.
  Incidentally, CLC will clear the carry bit.

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Indexed Addressing Mode

• LDX 0050
• LDAA 0,X
• ADDA 1,X
• SWI
• Program adds two numbers stored in memory
  locations 0050 and 0051

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D-bug12 Assembler
ASM 2000 Begin assembly at address 2000
End Assembly LOAD Load S-Records into
memory MD Memory Display MM Modify
Memory RD Display CPU registers RM
Modify CPU Register Contents PC 2000 loads 2000
into PC T Trace (single-step)