Transcript 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.
• 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.
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?
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
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
Moore’s Law
The number of transistors on a chip doubles every 18 months
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.
Memory
• Big Endian: 4 bytes arranged as:0123 (32-bit word)
• Little Endian: 4 bytes arranged 3210 (32-bit word)
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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
ROM
• ROM
• PROM
• EPROM - UV erasable
• EEPROM - Electrically erasable byte at a time
• FLASH - electrical block erasable - digital film - more like RAM!
HCS12 Data Sheet
http://www.freescale.com/files/microcontrollers/doc/data_sheet/H
CS12DFAMILYPP.pdf
HCS12 Architecture
A
B
A+B=D
X
Y
SP
PC
CCR
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
My First Program
 CLRA
 INC A
 SWI
Clears accumulator A ( A = 0 )
This instruction does this: A + 1
Stop (software interrupt)
A
Op-codes
Assembly Language
CLRA
INCA
SWI
Memory Location
2000
2001
2002
Op-codes
87
42
3F
My Second Program
LDAA # $ 12
ADDA # $ 15
SWI
Object Code . . . Program # 2
Assembly Language
Memory Location
Op-codes
LDAA # $ 12
2000
2001
86
12
ADDA # $ 15
2002
2003
8B
15
SWI
2004
3F
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
Immediate and Direct Modes
 Immediate LDAA # $ 12
 op-code
86 12
Load the hex number 12
 Direct LDAA $ 12
 op-code
96 12
Load from memory location 0012
My Third Program
Assembly Language
LDAA # $ 04
STAA $ 15
LDAA # $ 08
ADDA $ 15
SWI
Memory Location
?
Op-codes
?
My Third Program
Assembly Language
LDAA # $ 04
STAA $ 15
LDAA # $ 08
ADDA $ 15
SWI
Memory Location
2000
2002
2004
2006
2008
Op-codes
86
97
86
9B
3F
04
15
08
15
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
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 ?
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
Index Register
X is a 16-bit register
How are the following three instructions different?
LDX # $ 5C42
LDX $ 5C42
LDX $ 5C
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
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
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
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.
Examples Galore
 ADDA
The outcome is A + M
 ADDA # $ 2B
8B 2B
 ADDA $ 3C
9B 3C
 ADDA $ 5B24
AB 5B 24
A
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.
Indexed Addressing Mode
LDX # $ 0050
LDAA 0,X
ADDA 1,X
SWI
Program adds two numbers stored in memory locations 0050 and
0051
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)