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Physics 413 Chapter 1 : Introduction to the HCS 12 Microcontroller

Physics 413 Chapter 1 : Introduction to the HCS 12 Microcontroller. Computer Architecture. What is a Digital Computer ? A computer is essentially a fast electronic calculating machine.

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Physics 413 Chapter 1 : Introduction to the HCS 12 Microcontroller

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  1. Physics 413Chapter 1: Introduction to the HCS 12 Microcontroller

  2. 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 > 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.

  3. 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?

  4. 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

  5. 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

  6. Moore’s Law The number of transistors on a chip doubles every 18 months

  7. 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.

  8. Memory • Big Endian: 4 bytes arranged as:0123 (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

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

  10. HCS12 Data Sheet http://www.freescale.com/files/microcontrollers/doc/data_sheet/HCS12DFAMILYPP.pdf

  11. HCS12 Architecture A B A + B = D X Y SP PC CCR

  12. 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

  13. My First Program • CLRA Clears accumulator A ( A = 0 ) • INC A This instruction does this: A + 1 A • SWI Stop (software interrupt)

  14. Op-codes Assembly LanguageMemory LocationOp-codes CLRA 2000 87 INCA 2001 42 SWI 2002 3F

  15. My Second Program LDAA # $ 12 ADDA # $ 15 SWI

  16. Object Code . . . Program # 2 Assembly LanguageMemory LocationOp-codes LDAA # $ 12 2000 86 2001 12 ADDA # $ 15 2002 8B 2003 15 SWI 2004 3F

  17. 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

  18. 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

  19. My Third Program Assembly LanguageMemory LocationOp-codes LDAA # $ 04 STAA $ 15 LDAA # $ 08 ? ? ADDA $ 15 SWI

  20. My Third Program Assembly LanguageMemory LocationOp-codes LDAA # $ 04 2000 86 04 STAA $ 15 2002 97 15 LDAA # $ 08 2004 86 08 ADDA $ 15 2006 9B 15 SWI 2008 3F

  21. 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

  22. 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 ?

  23. 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

  24. Index Register X is a 16-bit register How are the following three instructions different? LDX # $ 5C42 LDX $ 5C42 LDX $ 5C

  25. 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

  26. 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 X+4

  27. 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

  28. Move it! • Memory to memory transfer • movb $1000,$2000 copies the (8-bit)contents of memory location $1000 to the memory location $2000 • movw0,X,0,Ycopies the 16-bit word pointed to by X to the memory location pointed to by Y.

  29. Examples Galore • ADDA The outcome is A + M A • ADDA # $ 2B8B 2B • ADDA $ 3C9B 3C • ADDA $ 5B24AB 5B 24

  30. 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.

  31. Indexed Addressing Mode LDX # $ 0050 LDAA 0,X ADDA 1,X SWI Program adds two numbers stored in memory locations 0050 and 0051

  32. 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)

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