Microprocessor Systems and Instrumentation

1

• Microprocessor Systems and Instrumentation
• SOE2121

2

• Microprocessor Systems and Instrumentation
• SOE2121
• Number Systems

3

• Machine code
• 01010011010100101010010010101001010010010000111100
  01010011001001010010100010001001010101001001001010
  01010000101010101001011100010111000100101010001010
  01000100101001010100100101000100010010100010101001
  00101001010000101010101001011100010111000100101010
  00101001000100101001010100100101000100010010100010
  10100100101001010000101010101001011100010111000100
  10101000101001000100101001010100100101000100010011
  00100101000100010011001001010001000100110010010100
  01000100110010010100010001001010001010100100101001
  01000010101010100101110001011100010010101000101001
  00010010100101010010010100010001001010001010100011
  11100100101001001010010100001000100010010111

4

• Machine code
• 01010001 01010010 10100100 10101001 01001001
  00001111 00010100 11001001 01001010 00100010
  01010101 00100100 10100101 00001010 10101001
  01110001 01110001 00101010 00101001 00010010
  10010101 00100101 00010001 00101000 10101001
  00101001 01000010 10101010 01011100 01011100
  01001010 10001010 01000100 10100101 01001001
  01000100 01001010 00101010 01001010 01010000
  10101010 10010111 00010111 00010010 10100010
  10010001 00101001 01010010 01010001 00010011
  00100101 00010001 00110010 01010001 00010011
  00100101 00010001 00110010 01010001 00010010
  10001010 10010010 10010100 00101010 10100101
  11000101 11000100 10101000 10100100 01001010

5

• Machine code
• DB 33 37 56 5E 4B 67 85 44 34 77 62 A3 D9 FF 03
  74 64 EE E7 F2 83 82 99 55 64 EE E7 F2 83 82 99
  55 64 EE E7 F2 83 82 99 55 64 EE E7 F2 83 82 99
  55 64 EE E7 F2 83 82 99 55 64 EE E7 F2 83 82 99
  55 64 EE E7 F2 83 82 99 55 99 55 64 EE E7 F2 83
  82 99 55 99 55 64 EE E7 F2 83 82 99 55 99 55 64
  EE E7 F2 83 82 99 55 99 55 64 EE E7 F2 83 82 99
  55 99 55 64 EE E7 F2 83 82 99 55 99 55 64 EE E7
  F2 83 82 99 55 99 55 64 EE E7 F2 83 82 99 55 99
  55 64 EE E7 F2 83 82 99 55 99 55 64 EE E7 F2 83
  82 99 55 76 F5 E2 AB 72 97 43...

6

• The Decimal System
• Decimal Number 38O7 3 x
  1OOO ( 1O3) 3OOO
  8 x 1OO ( 1O2) 8OO
  O
  x 1O ( 1O1) OO
  7 x 1 ( 1OO)
  7 ----
  Total 38O7

7

• The Binary System
• Binary Number 1O11
  1 x 8 (
  23) 8
  O x 4 ( 22) O
  1 x 2 (
  21) 2
  1 x 1 ( 2O) 1
  
  --
  Total 11

8

• The Binary System
• 
  Bit value
  128 64 32 16 8 4 2 1
  Power of 2 27 26 25 24
  23 22 21 2O
• Number
  1 0 0 1 0 1 1 0

9

• The Decimal and Binary Systems
• Decimal Number 38O7 3 x
  1OOO ( 1O3) 3OOO 8 x 1OO (
  1O2) 8OO O x 1O ( 1O1) OO
  7 x 1 ( 1OO) 7
  ----
  Total 38O7
• Binary Number 1O11 1 x 8
  ( 23) 8 O x 4 ( 22)
  O 1 x 2 ( 21) 2 1
  x 1 ( 2O) 1
  -- Total 11

10

• The Hexadecimal System
• Hexadecimal Number 21AF (Base 16)
  
  2 x 4O96 ( 163) 8192
  1
  x 256 ( 162) 256
  A x 16 ( 161)
  16O
  F x 1 ( 16O) 15
  ---- Total
  8623

11

• Number Systems
• Decimal Numbers (Base 1O) 1O symbols
  O
  1 2 3 4 5 6 7 8 9
  Binary Numbers (Base 2) 2
  symbols
  O 1
  Hexadecimal
  Numbers(Base 16) 16 symbols
  O 1 2 3 4
  5 6 7 8 9 A B C D E F
  
  

12

• Brain Exercises (Neurobics)
• Binary counting on fingers (and toes
  after ?)
• Binary Arithmetic -
  Addition -
  Subtraction / Division
  Multiplication
  
• Hexadecimal Arithmetic -
  Addition -
  Subtraction / Division
  Multiplication
  

13

• HEX BINARY DECIMAL
  O OOOO
  O 1 OOO1 1
  2 OO1O 2
  3 OO11 3 4
  O1OO 4 5 O1O1
  5 6 O11O 6
  7 O111 7
  8 1OOO 8 9
  1OO1 9 A 1O1O
  1O B 1O11 11
  C 11OO 12
  D 11O1 13 E
  111O 14 F 1111
  15

14

• Converting between Binary and Hexadecimal
• Binary 0010 1100 328444
• Hex 2 C 321244
  

15

• Converting between Binary and Hexadecimal
• 111O1OO111O1 111O 1OO1 11O1
  E 9 D
  12AB 1 2 A
  B OOO1 OO1O 1O1O 1O11

16

• Number conversions - Hex to Decimal
• Convert 1234 hex to decimal
• 163 162 161 160
• 4096 256 16 1
• 1 2 3 4
• 1 x 4096 4096
• 2 x 256 512
• 3 x 16 48
• 4 x 1 4
• -----

17

• Number conversions - Decimal to Binary
• Convert 1234 decimal to binary
• 210 1024 - 1 1234 - 1024 210
• 29 512 - 0
• 28 256 - 0
• 27 128 - 1 210 - 128 82
• 26 64 - 1 82 - 64 18
• 25 32 - 0
• 24 16 - 1 18 - 16 2
• 23 8 - 0
• 22 4 - 0
• 21 2 - 1 2 - 2 0
• 20 1 - 0
• So 1234 decimal 100 1101 0010 binary

18

• Number conversions - Binary to Hex
• eg binary number 11010011101011010
• First divide up FROM THE RIGHT into groups of 4
  bits
• 1 1010 0111 0101 1010
• Then use the hex table (or better your brain)
  to
• write the hex values
• 1 1010 0111 0101 1010
• 1 A 7 5 A
• Note learn 0-9 and remember A1010 and
  C1100

19

• HEX BINARY DECIMAL
  O OOOO
  O 1 OOO1 1
  2 OO1O 2
  3 OO11 3 4
  O1OO 4 5 O1O1
  5 6 O11O 6
  7 O111 7
  8 1OOO 8 9
  1OO1 9 A 1O1O
  1O B 1O11 11
  C 11OO 12
  D 11O1 13 E
  111O 14 F 1111
  15

20

• Negative Numbers - Twos Complement form
• To form a negative number, for example -3, first
  invert (ones complement) the positive number of
  the same magnitude (3), then add one
• 00000011 3
• invert to give
• 11111100 ones complement
• 00000001 add one
• --------
• 11111101 result is -3 (Hex FD)

21

• Negative Numbers
• Most negative number
• -128
• Most positive number
• 127
• Note bit 7 carries the sign information
• 1negative 0positive

7
0
0
0
0
0
0
0
0
1
7
0
1
1
1
1
1
1
1
0
22

• Negative Numbers
• 0111 1111 7F 127
• 0111 1110 7E 126
• 0000 0011 03 3
• 0000 0010 02 2
• 0000 0001 01 1
• 0000 0000 00 0
• 1111 1111 FF -1
• 1111 1110 FE -2
• 1111 1101 FD -3
• 1000 0001 81 -127
• 1000 0000 80 -128

23

• Signed and Unsigned Arithmetic
• Why does it work for both unsigned numbers (0 to
  255) and signed numbers (-128 to 127)?
• Unsigned Data Signed
• 253 FD -3
• 1 01 1
• --- --- ---
• 254 FE -2

24

• Binary Coded Decimal
• Each decimal digit is encoded as a 4 bit binary
  number
• O OOOO 1
  OOO1 2 OO1O
  3 OO11
  4 O1OO 5
  O1O1 6 O11O
  7 O111
  8 1OOO 9
  1OO1
• eg decimal 42 0100 0010
• 4 2
• What is this value in Hexadecimal?
• (Note 42 in binary is 0010 1010
  Hex 2A)

25

• Binary Coded Decimal
• Range of BCD numbers in one byte 00 - 99
• Reading a BCD number in hex gives the decimal
  value

26

• HEX BINARY DECIMAL
  O OOOO
  O 1 OOO1 1
  2 OO1O 2
  3 OO11 3 4
  O1OO 4 5 O1O1
  5 6 O11O 6
  7 O111 7
  8 1OOO 8 9
  1OO1 9 A 1O1O
  1O B 1O11 11
  C 11OO 12
  D 11O1 13 E
  111O 14 F 1111
  15

27

• ASCII Table
• MSD-gt0 1 2 3 4 5 6 7
• LSD
• 0 NUL DLE SP 0 _at_ P p
• 1 SOH DC1 ! 1 A Q a q
• 2 STX DC2 " 2 B R b r
• 3 ETX DC3 3 C S c s
• 4 EOT DC4 4 D T d t
• 5 ENQ NAK 5 E U e u
• 6 ACK SYN 6 F V f v
• 7 BEL ETB ' 7 G W g w
• 8 BS CAN ( 8 H X h x
• 9 HT EM ) 9 I Y i y
• A LF SUB J Z j z
• B VT ESC K k
• C FF FS , lt L l
• D CR GS - M m
• E SO RS . gt N n

28

• The Byte
• 7 6 5 4 3 2 1 0
• 1 Byte 8 bits
• Contains one of 256 possible patterns
  
  OOOOOOOO
  OOOOOOO1
  OOOOOO1O OOOOOO11
  OOOOO1OO
  
  11111111
• Range OO-FF
  O to 255

29

• The Byte
• 7 6 5 4 3 2 1 0

Most Significant Bit
Least Significant Bit
30

• Which is Most Significant?
• A typical lecturers salary might be
• 93,878

Least Significant Digit
Most Significant Digit
31

• Hexadecimal Representation
• Binary Hex Meaning Value
• 0100 0001 41 Unsigned Binary 65 Decimal
• 0100 0001 41 ASCII code A
  
• 0100 0001 41 BCD number 41 Decimal
• 1111 1111 FF Signed Binary -1 Decimal
  
• 1111 1111 FF Unsigned Binary 255 Decimal
  
• 1010 0101 A5 Opcode LDA

7 6 5 4 3 2 1 0
32

• Brain Exercises (Neurobics)
• Binary counting on fingers (and toes
  after ?)
• Binary Arithmetic -
  Addition -
  Subtraction / Division
  Multiplication
  
• Hexadecimal Arithmetic -
  Addition -
  Subtraction / Division
  Multiplication
  

33

• Introduction
• Load and Store
• Transfer

34

• Not Recommended Book
• 65O2 Assembly Language Programming
  
• by L A Leventhal
  
• Pub Osborne/McGraw-Hill

35

• Assembly Language
• Advantages
• Fastest possible program (on a particular
  processor)
• Smallest size program (cheaper ROM)
• Smallest RAM requirement (cheaper RAM)
  Disadvantages
• Much longer software development time
• Programs more difficult to debug
• Programs not portable

36

• Assembly Language When is it used?
• MASS PRODUCTIONWhere the lowest possible
  production cost is required and longer more
  expensive software development time is
  acceptable. eg microwave oven,
  mobile phone
• HIGH SPEED APPLICATIONSWhere a high level
  language would not respond quickly enough.
  eg high speed data acquisition system
• Notes faster processors, critical bits in
  assembler, smallest physical size
• eg Pacemaker where power consumption
  is also a consideration.

37

• Microprocessor Systems and Instrumentation
• SOE2121
• Number Systems

38

• Machine code
• 01010011010100101010010010101001010010010000111100
  01010011001001010010100010001001010101001001001010
  01010000101010101001011100010111000100101010001010
  01000100101001010100100101000100010010100010101001
  00101001010000101010101001011100010111000100101010
  00101001000100101001010100100101000100010010100010
  10100100101001010000101010101001011100010111000100
  10101000101001000100101001010100100101000100010011
  00100101000100010011001001010001000100110010010100
  01000100110010010100010001001010001010100100101001
  01000010101010100101110001011100010010101000101001
  00010010100101010010010100010001001010001010100011
  11100100101001001010010100001000100010010111

39

• Machine code
• 01010001 01010010 10100100 10101001 01001001
  00001111 00010100 11001001 01001010 00100010
  01010101 00100100 10100101 00001010 10101001
  01110001 01110001 00101010 00101001 00010010
  10010101 00100101 00010001 00101000 10101001
  00101001 01000010 10101010 01011100 01011100
  01001010 10001010 01000100 10100101 01001001
  01000100 01001010 00101010 01001010 01010000
  10101010 10010111 00010111 00010010 10100010
  10010001 00101001 01010010 01010001 00010011
  00100101 00010001 00110010 01010001 00010011
  00100101 00010001 00110010 01010001 00010010
  10001010 10010010 10010100 00101010 10100101
  11000101 11000100 10101000 10100100 01001010

40

• Machine code
• DB 33 37 56 5E 4B 67 85 44 34 77 62 A3 D9 FF 03
  74 64 EE E7 F2 83 82 99 55 64 EE E7 F2 83 82 99
  55 64 EE E7 F2 83 82 99 55 64 EE E7 F2 83 82 99
  55 64 EE E7 F2 83 82 99 55 64 EE E7 F2 83 82 99
  55 64 EE E7 F2 83 82 99 55 99 55 64 EE E7 F2 83
  82 99 55 99 55 64 EE E7 F2 83 82 99 55 99 55 64
  EE E7 F2 83 82 99 55 99 55 64 EE E7 F2 83 82 99
  55 99 55 64 EE E7 F2 83 82 99 55 99 55 64 EE E7
  F2 83 82 99 55 99 55 64 EE E7 F2 83 82 99 55 99
  55 64 EE E7 F2 83 82 99 55 99 55 64 EE E7 F2 83
  82 99 55 76 F5 E2 AB 72 97 43...

41

• HEX BINARY DECIMAL
  O OOOO
  O 1 OOO1 1
  2 OO1O 2
  3 OO11 3 4
  O1OO 4 5 O1O1
  5 6 O11O 6
  7 O111 7
  8 1OOO 8 9
  1OO1 9 A 1O1O
  1O B 1O11 11
  C 11OO 12
  D 11O1 13 E
  111O 14 F 1111
  15

42

• The Byte
• 7 6 5 4 3 2 1 0
• 1 Byte 8 bits
• Contains one of 256 possible patterns
  
  OOOOOOOO
  OOOOOOO1
  OOOOOO1O OOOOOO11
  OOOOO1OO
  
  11111111
• Range OO-FF
  O to 255

43

• The Byte
• 7 6 5 4 3 2 1 0

Most Significant Bit
Least Significant Bit
44

• Which is Most Significant?
• A typical lecturers salary might be
• 93,878

Least Significant Digit
Most Significant Digit
45

• The Byte
• 7 6 5 4 3 2 1 0
• 1 Byte 8 bits
• Contains one of 256 possible patterns
  
  OOOOOOOO
  OOOOOOO1
  OOOOOO1O OOOOOO11
  OOOOO1OO
  
  11111111
• Range OO-FF
  O to 255

46

• Hexadecimal Representation
• Binary Hex Meaning Value
• 0100 0001 41 Unsigned Binary 65 Decimal
• 0100 0001 41 ASCII code A
  
• 0100 0001 41 BCD number 41 Decimal
• 1111 1111 FF Signed Binary -1 Decimal
  
• 1111 1111 FF Unsigned Binary 255 Decimal
  
• 1010 0101 A5 Opcode LDA

7 6 5 4 3 2 1 0
47

• 6502 Programmers Model

Memory
7 0
Microprocessor
FFFF 0200 01FF 0100 00FF 0000
7 0
A
X
Y
15 8
PC
00000001
SP
NV-BDIZC
STACK
PS
PAGE ZERO
48

• Memory
• 65536 bytes numbered
• in decimal O - 65535
  in hex OOOO - FFFF
  in binary OOOO OOOO OOOO OOOO - 1111
  1111 1111 1111
  
• The number of each memory location is known as
  its ADDRESS
  2 Bytes are required to hold an
  address which is 16 bits

49

• Instruction Formats

One byte instructions
OPCODE
Two byte instructions
OPCODE
OPERAND
Three byte instructions
OPCODE
OPER
AND
50

• Load and Store Instructions

51

• The LDA Instruction
• Copy the contents of memory location 8O into
• the A register
  LDA 8O
  
  This
  instruction uses zero page addressing since
  address 8O is on page zero
  

52

• The LDA Instruction and the Instruction Set Sheet
  
• Assembly Language LDA 8O Machine
  Code A5 8O
  Instruction Set Sheet Entry
  A5 3
  Opcode A5 Time 3
  clock cycles Length 2 bytes
  

53

• The LDA Instruction and the Instruction Set Sheet
  
• ----------------------------------------
  ----- Immed ABS ZP
  Effect on Operation
  len2len3len2the flags
  OP nOP nOP n NV-BDIZC
  ------------------------------------------
  ----
• LDA A M A9 2AD 4A5 3
  N.....Z.
• Assembly Language LDA 8O Machine
  Code A5 8O
  Instruction Set Sheet Entry
  A5 3
  Opcode A5 Time 3
  clock cycles Length 2 bytes
  

54

• The LDA Instruction and the Instruction Set Sheet
  
• Assembly Language LDA 8O Machine
  Code A5 8O Instruction Set
  Sheet Entry A5 3 Opcode A5 Time 3 clock
  cycles Length 2 bytes
• Effect on the Flags N.....Z.
• N and Z changed depending on the value that is
  loaded
• The N flag
  becomes the sign bit (7) of the value loaded
  The Z flag is
  1 if the value loaded is zero The Z flag is O
  if the value loaded is not zero

55

• Load and Store instructions
• Absolute Zero Page
• LDA 1234 LDA 8O
  
• STA 1234 STA 8O
  
  LDX 1234 LDX 8O
  
  STX 1234 STX 8O
  
  LDY 1234 LDY 8O
  
  STY 1234 STY 8O

56

• Immediate Addressing
• Instruction Machine code
  LDA AA
  A9 AA
  LDX FF A2 FF
  LDY
  O1 AO O1

57

• Dont mix these up!
• Zero Page LDA OO
  
  
  Immediate LDA OO

58

• Transfer Instructions

59

• Transfer instructions
  
• TAX Copy register A to register X
  
  The old value in X is lost Register A is not
  affected
  
  
  

60

• Transfer instructions
  
• TAX TAY TXA TYA
• (TXS TSX)
• All 1 byte Long
  Implied Addressing 2
  Clock Cycles Flags as
  for LDA

61

• Arithmetic
• Instructions
• ADC SBC

62

• Negative Numbers

63

• Negative Numbers - Twos Complement form
• To form a negative number, for example -3, first
  invert (ones complement) the positive number of
  the same magnitude (3), then add one
• 00000011 3
• invert to give
• 11111100 ones complement
• 00000001 add one
• --------
• 11111101 result is -3 (Hex FD)

64

• Negative Numbers
• Most negative number
• -128
• Most positive number
• 127
• Note bit 7 carries the sign information
• 1negative 0positive

7
0
0
0
0
0
0
0
0
1
7
0
1
1
1
1
1
1
1
0
65

• Signed and Unsigned Arithmetic
• Why does it work for both unsigned numbers (0 to
  255) and signed numbers (-128 to 127)?
• Unsigned Data Signed
• 253 FD -3
• 1 01 1
• --- --- ---
• 254 FE -2

66

• ADC

67

• Addition
• CLC
• LDA 8O
  ADC 81
  STA 82

68

• Two byte arithmetic
• How do we do it in decimal?
• 36
• 25
• ---
• 61

69

• Addition and Subtraction
• CLC SEC
  LDA 8O
  LDA 8O
  ADC 81 SBC 81
  STA
  82 STA 82

70

• Two byte arithmetic

First Number
Second Number
Result
LSB
LSB
LSB
MSB
MSB
MSB
80
81
82
83
84
85
Addition
Subtraction
CLC SEC LDA 8O LSBs LDA
8O LSBs ADC 82 SBC 82
STA 84 STA 84 LDA
81 MSBs LDA 81 MSBs ADC 83
SBC 83 STA 85
STA 85
71

• Decimal Arithmetic

72

• 6502 Programmers Model

Memory
7 0
Microprocessor
FFFF 0200 01FF 0100 00FF 0000
7 0
A
X
Y
15 8
PC
00000001
SP
NV-BDIZC
STACK
PS
PAGE ZERO
73

• Decimal Arithmetic (BCD)
• SED SED CLC
  SEC LDA 8O
  LDA 8O ADC 81 SBC 81
  STA 82 STA 82
  CLD CLD

Addition
Subtraction
74

• Logical Instructions

75

• Logical Operations
  

76

• Logical Operations
  And
  AND

77

• Logical Operations
  And
  AND Or ORA
  

78

• Logical Operations
  And
  AND Or ORA
  Exclusive Or EOR

79

• AND

80

• The AND Instruction
  
  LDA A9 1O1O 1OO1
  (A) AND OF OOOO 1111 (M)
  ---------
  Result OOOO 1OO1
  
  Any O in the mask will clear the
  corresponding bit in A to O
• Any 1 in
  the mask will leave the corresponding bit in A
  unchanged

81

• OR

82

• The ORA Instruction
  
  LDA A9 1O1O 1OO1
  (A) ORA OF OOOO 1111 (M)
  ---------
  Result 1010 1111
  
  Any 1 in the mask will set the corresponding bit
  in A
• to 1
• Any 0 in
  the mask will leave the corresponding bit in A
  unchanged

83

• EOR

84

• The EOR Instruction
  
  LDA A9 1O1O 1OO1
  (A) EOR OF OOOO 1111 (M)
  ---------
  Result 1010 0110
  
  Any 1 in the mask will invert the corresponding
  bit in A
• (so 1 becomes 0 and 0 becomes 1)
• Any 0 in
  the mask will leave the corresponding bit in A
  unchanged

85

• Testing individual bits in a byte

86

• Testing Individual Bits in a Byte To test
  bit 2 of location 8O
  LDA 8O byte to test
  AND O4 mask OOOO O1OO

87

• The Byte
• 7 6 5 4 3 2 1 0
• 0 0 0 0 0 1 0 0
• Hex 04

?
88

• Testing Individual Bits in a Byte eg - to
  test bit 2 of location 8O
  LDA 8O byte to
  test AND O4 mask OOOO O1OO
  

89

• Testing Individual Bits in a Byte eg - to
  test bit 2 of location 8O
  LDA 8O byte to
  test AND O4 mask OOOO O1OO
  8O contains B7
  A 1O11 O111
  M OOOO O1OO ---------
  OOOO O1OO
  Z flag O
  

90

• Testing Individual Bits in a Byte eg - to
  test bit 2 of location 8O
  LDA 8O byte to
  test AND O4 mask OOOO O1OO
  8O contains B7 8O contains 69
  A
  1O11 O111 A O11O 1OO1 M OOOO O1OO
  M OOOO O1OO ---------
  --------- OOOO O1OO OOOO OOOO
  
  Z flag O Z flag 1

91

• The BIT Instruction (this is rather
  a funny instruction)
  eg LDA O1 mask
  for AND BIT 8O byte to test
  
• Z is set by the result of the AND
  
  1OO1 1OO1 OOOO OOO1
  ---------
  OOOO OOO1 ie non-zero so
  Z O

7 6 5 4 3 2 1 0
1
0
0
1
1
0
0
1
N V
92

• Logical instructions - Example
• LDA 33 Result is OO11 OO11 33
  AND OF
  ORA 9O
  EOR 8O
  EOR FF
  

93

• Logical instructions - Example
• LDA 33 Result is OO11 OO11 33
  AND OF
  Result is OOOO OO11 O3
  ORA 9O
  EOR 8O
  EOR FF
  

94

• Logical instructions - Example
• LDA 33 Result is OO11 OO11 33
  AND OF
  Result is OOOO OO11 O3
  ORA 9O Result is 1OO1
  OO11 93
  EOR 8O
  EOR FF
  

95

• Logical instructions - Example
• LDA 33 Result is OO11 OO11 33
  AND OF
  Result is OOOO OO11 O3
  ORA 9O Result is 1OO1
  OO11 93
  EOR 8O Result is OOO1 OO11 13
  EOR FF
  

96

• Logical instructions - Example
• LDA 33 Result is OO11 OO11 33
  AND OF
  Result is OOOO OO11 O3
  ORA 9O Result is 1OO1
  OO11 93
  EOR 8O Result is OOO1 OO11 13
  EOR FF
  Result is 111O 11OO EC
  

97

• Shift and Rotate Instructions

98

• Shift and Rotate Instructions
  
  
  ASL

99

• Shift and Rotate Instructions
  
  
  ASL LSR

100

• Shift and Rotate Instructions
  
  
  ASL LSR ROL
  

101

• Shift and Rotate Instructions
  
  
  ASL LSR ROL ROR
  

102

• The ASL instruction The bits in the
  byte are shifted one position to the left
  A zero is shifted into bit O Bit 7 is
  shifted out into the carry flag
  
• eg ASL 42 ASL 21OF
  ASL A New Addressing
  Mode!

C
7
0
0
103

• The LSR instruction The bits in the
  byte are shifted one position to the right
  A zero is shifted into bit 7 Bit 0 is
  shifted out into the carry flag
  
• eg LSR 42 LSR 21OF
  LSR A

C
7
0
0
104

• The ASL instruction
  

C
7
0
0
0
1
0
0
0
0
0
0
105

• The ASL instruction
  

C
7
0
0
0
0
1
0
0
0
0
0
106

• The ASL instruction
  

C
7
0
0
0
0
0
1
0
0
0
0
107

• The ASL instruction
  

C
7
0
0
0
0
0
0
1
0
0
0
108

• The ASL instruction
  

C
7
0
0
0
0
0
0
0
1
0
0
109

• The ASL instruction
  

C
7
0
0
0
0
0
0
0
0
1
0
110

• The ASL instruction
  

C
7
0
0
0
0
0
0
0
0
0
1
111

• The ASL instruction
  

C
7
0
1
0
0
0
0
0
0
0
0
112

• The ASL instruction
  

C
7
0
0
0
0
0
0
0
0
0
0
113

• The ROL instruction The bits in the
  byte are shifted one position to the left
  The original value of the carry is shifted
  into bit O Bit 7 is shifted out into
  the carry flag
  
• 
  

C
7
0
114

• The ROR instruction The bits in the
  byte are shifted one position to the right
  The original value of the carry is shifted
  into bit 7 Bit 0 is shifted out into
  the carry flag
  
• 
  

C
7
0
115

• eg
  LSR 80 msb
• ROR 81 lsb
• 80
  81
• 
  

2 Byte Shift
7 6 5 4 3 2 1 0
7 6 5 4 3 2 1 0
1
0
0
1
1
0
0
1
1
0
0
1
1
0
0
1
0
C
1
116

• Jumping and Branching and Comparing

117

• Unconditional Jump - JMP
• 
  O25O CLC O251 LDA
  4O O253 ADC 41
  O255 STA 42
  --O257 JMP O25E
  O25A LDA 8O O25C STA
  81 --O25E LDA FOFA
  O261 STA 35
  

118

• Conditional Branch Instructions
• BNE
  Branch if not equal to zero Z OBEQ Branch if
  equal to zero Z 1
  BCC Branch if carry clear
  C OBCS Branch if carry set C 1
  BPL
  Branch if plus (positive) N OBMI Branch
  if minus (negative) N 1
  (BVC Branch if overflow
  clear V O)(BVS Branch if overflow set
  V 1)

119

• Conditional Branch Instructions
• O25O LDA 8O
  --O252 BNE O256
  O254 LDA 81 --O256 STA
  82 O258 BRK
  O25O A5 (LDA) -4 FC
  O251 8O -3 FD O252
  DO (BNE) -2 FE O253 O2
  -1 FF O254 A5 (LDA) O
  OO O255 81 1 O1
  O256 85 (LDA) 2 O2 O257
  82 3 O3 O258 OO (BRK)
  4 O4

120

• Delay Loop 10s
  
• O4OO LDA 12 12 18 decimal
  O4O2 STA 82 O4O4 LDA
  OO O4O6 STA 8O
  O4O8 STA 81
  O4OA DEC 8O O4OC
  BNE O4OA inner loop O4OE DEC 81
  O41O BNE O4OA next
  loop O412 DEC 82
  O414 BNE O4OA outer loop O416
  RTS

121

• Comparing

CMP CPX CPY
122

• Compare Instructions
  CMP
  CPX CPY
• Examples
• CMP 8O CPX 8O CPY 8O CMP
  1234 CPX 1234 CPY 1234 CMP O3
  CPX O3 CPY O3
  The Z and C flags are changed after a
  compare instruction as follows
  A M
  then Z 1 (BEQ will branch) A ltgt M then
  Z O (BNE will branch)
  A gt M then C 1 (BCS will
  branch) A lt M then C O (BCC will
  branch)

123

• To compare the contents of 5O and 51
  
• O25O LDA 5O first number O252
  CMP 51 second number O254 BEQ O26O
  branch if firstsecond O256 BCS O27O branch if
  firstgtsecond O258 BCC O28O branch if
  firstltsecond O25A
  O26O
  here if firstsecond
  O27O here if
  firstgtsecond
  O28O here if firstltsecond

124

• Loops and Indexed addressing

125

• Incrementing
• and
• Decrementing

126

• Incrementing and Decrementing
  
  Memory Locations
  
  INC 8O DEC 2F
  INC O412
  DEC 12BA Registers
  
  INX DEX
  INY DEY
  

127

• Car Mileometer
• What happens if you drive forward one more
  mile?

9
9
9
9
9
128

• Car Mileometer
• What happens if you reverse one mile?

0
0
0
0
0
129

• Decrementing X
• Instruction Value of X after
  instruction
• 04 DEX
  O3 DEX O2
  DEX O1
  DEX OO (Z flag
  set) DEX FF
  DEX FE
  DEX FD
  

130

• Incrementing X
• Instruction Value of X after
  instruction
• FC INX
  FD INX FE
  INX FF
  INX OO (Z flag
  set) INX 01
  INX 02
  INX 03
  

131

• Looping

132

• Loop Example add the contents of
  locations 80 to 85
• 
  O25O LDA
  OO A will hold sum O252 LDX OO X -
  loop counter O254 CLC
  -O255 ADC 8O,X Add next byte
  O257 INX O258 CPX
  O6 Have we finished? -O25A BNE O255 If
  not continue O25C STA 8A Store the sum
  O25E BRK

80 81 82 83 84 85
86 87
133

• Indexed Addressing

134

• Indexed Addressing
  
• 
  Zero Page,X ADC 8O,X
  
  Zero Page,Y LDX 8O,Y
  Absolute,X
  LDA 123A,X
  Absolute,Y LDA 456B,Y
  

135

• Delay Loop 10ms
  
  
  O3OO LDY OAouter loop 1O times O3O2 LDX
  C8inner loop 2OO times O3O4 DEX
  O3O5 BNE O3O4
  O3O7 DEY O3O8
  BNE O3O2 O3OA RTS
  
  

136

• Delay Loop 10s
  
• O4OO LDA 12 12 18 decimal
  O4O2 STA 82 O4O4 LDA
  OO O4O6 STA 8O
  O4O8 STA 81
  O4OA DEC 8O O4OC
  BNE O4OA inner loop O4OE DEC 81
  O41O BNE O4OA next
  loop O412 DEC 82
  O414 BNE O4OA outer loop O416
  RTS

137

• The NOP Instruction
• NOP does nothing
• 1 byte 2 clock cycles

138

• Subroutines and the Stack

139

• Subroutines
• 0200 LDA 94
• AND 07
• JSR 0500
• 0207 LDA 94 0500 LDA 80
• ORA 80 AND 0F
• JSR 0500 RTS
• 020E LDX 08
• JSR 0500
• 0213 STA 60,X
• DEX

140

• Subroutines
• JSR 0500
• RTS

141

• The Stack

01FF
A1
01FE
35
SP
01
FF
01FD
29
01FC
81
01FB
12
01FA
7B
01F9
5D


0100
142

• Push and Pull Instructions
• Register A
• PHA store on stack
• PLA get from stack
• Flag Register
• PHP store on stack
• PLP get from stack

143

• Subroutines

SP
01
FF
LDA 30 STA 51 CLC ADC 42 LSR A JSR 0400 CMP
05 BNE 0294 JMP 0280 LDA 50 ADC 42 LSR A CMP
05 BNE 0294 JMP 0280 LDA 50 STA 62 ROR 7E LDA
30 STA 51 CLC ADC 42 LSR A CMP 05 BNE 0294 JMP
0280 LDA 50 STA 62
0400
0250
LDA 30 STA 51 CLC ADC 42 LSR A JSR 0500 STA
9A LSR A STA 3B RTS
01FF
AA

01FE
F3
01FD
0262
29
0413
01FC
81
01FB
12
01FA
7B
0500
LSR A STA 6F STA 77 RTS
01F9
5D
Before First JSR
144

• The Stack

01FF
A1
01FE
35
SP
01
FF
01FD
29
01FC
81
01FB
12
01FA
7B
01F9
5D


0100
145

• The Stack
• Store the value AA on the stack

01FF
A1
01FE
35
SP
01
FF
01FD
29
01FC
81
01FB
12
01FA
7B
01F9
5D


0100
146

• The Stack
• Store the value AA on the stack

01FF
AA
01FE
35
SP
01
FE
01FD
29
01FC
81
01FB
12
01FA
7B
01F9
5D


0100
147

• The Stack
• Store the value F3 on the stack

01FF
AA
01FE
35
SP
01
FE
01FD
29
01FC
81
01FB
12
01FA
7B
01F9
5D


0100
148

• The Stack
• Store the value F3 on the stack

01FF
AA
01FE
F3
SP
01
FD
01FD
29
01FC
81
01FB
12
01FA
7B
01F9
5D


0100
149

• The Stack
• The Stack pointer always contains the
• address of the next free location

01FF
AA
01FE
F3
SP
01
FD
01FD
29
01FC
81
01FB
12
01FA
7B
01F9
5D


0100
150

• The Stack
• Get a byte from the stack

01FF
AA
01FE
F3
SP
01
FD
01FD
29
01FC
81
01FB
12
01FA
7B
01F9
5D


0100
151

• The Stack
• Get a byte from the stack
• The Stack Pointer is first
• incremented to point to the
• last value stored

01FF
AA
01FE
F3
SP
01
FE
01FD
29
01FC
81
01FB
12
01FA
7B
01F9
5D


0100
152

• The Stack
• Get a byte from the stack
• We get the value F3 -
• the last value stored
• 01FE is now the next free location

01FF
AA
01FE
F3
SP
01
FE
01FD
29
01FC
81
01FB
12
01FA
7B
01F9
5D


0100
153

• What happens when a subroutine is called before
  JSR
• 0260 JSR 0500
• 0263 LDA 00
• 0500 LDX 03
• 0502 TAY
• 0503 RTS

01FF
AA
01FE
F3
SP
01
FF
01FD
29
01FC
81
01FB
12
01FA
7B
01F9
5D
154

• What happens when a subroutine is called after
  JSR
• 0260 JSR 0500
• 0263 LDA 00
• 0500 LDX 03
• 0502 TAY
• 0503 RTS

01FF
02
01FE
62
SP
01
FD
01FD
29
01FC
81
01FB
12
01FA
7B
01F9
5D
155

• What happens when a subroutine is called after
  RTS
• 0260 JSR 0500
• 0263 LDA 00
• 0500 LDX 03
• 0502 TAY
• 0503 RTS

01FF
02
01FE
62
SP
01
FF
01FD
29
01FC
81
01FB
12
01FA
7B
01F9
5D
156

• Interrupts

157

• Interrupts
• Main Program LDA 30
• STA 51
• CLC
• ADC 42
• LSR A
• CMP 05
• BNE 0294
• JMP 0280 PHA
• LDA 50 LDA 33
• STA 62 STA 51
• ROR 7E LDA A000
• LDA 30 STA 80
• STA 51 LDA A001
• CLC STA 81
• ADC 42 INC 9A
• LSR A DEC 9B

Interrupt Routine
Interrupt occurs here
When an interrupt occurs, the return address is
stored on the stack, in the same way as for a
subroutine call. The contents of the flag
register is also stored on the stack.
158
5v

• 6502 Interrupt inputs

10K
___ IRQ ___ NMI ___ RES 6502 microprocessor
0v
159

• 6502 Vectors
• ___
• NMI FFFA FFFB ___ RES
  FFFC FFFD
• ___