Unit 2.ppt

Chapter 2
8085 Microprocessor and 8051
Microcontroller

Microprocessor Architecture
• The microprocessor can be programmed to
perform functions on given data by writing
specific instructions into its memory.
– The microprocessor reads one instruction at a
time, matches it with its instruction set, and
performs the data manipulation specified.
– The result is either stored back into memory or
displayed on an output device.
2

The 8085 Architecture
• The 8085 uses three separate busses to
perform its operations
– The address bus.
– The data bus.
– The control bus.
3

The Address Bus
– 16 bits wide (A0 A1…A15)
• Therefore, the 8085 can access locations with numbers from
0 to 65,536. Or, the 8085 can access a total of 64K addresses.
– “Unidirectional”.
• Information flows out of the microprocessor and into the
memory or peripherals.
– When the 8085 wants to access a peripheral or a
memory location, it places the 16-bit address on the
address bus and then sends the appropriate control
signals.
5

The Data Bus
– 8 bits wide (D0 D1…D7)
– “Bi-directional”.
• Information flows both ways between the
microprocessor and memory or I/O.
– The 8085 uses the data bus to transfer the binary
information.
– Since the data bus has 8-bits only, then the 8085
can manipulate data 8 bits at-a-time only.
6

The Control Bus
– There is no real control bus. Instead, the control
bus is made up of a number of single bit control
signals.
7

Operation Types in a Microprocessor
• All of the operations of the microprocessor
can be classified into one of three types:
- Microprocessor-Initiated Operations
- Internal Operations
- Peripheral-Initiated Operations
8

Microprocessor-Initiated Operations
• These are operations that the microprocessor
itself starts.
• These are usually one of 4 operations:
– Memory Read
– Memory Write
– I/O Read (Get data from an input device)
– I/O write (Send data to an output device)
9

Microprocessor-Initiated Operations
• It is important to note that the microprocessor treats
memory and I/O devices the same way.
– Input and output devices simply look like memory
locations to the microprocessor.
• For example, the keyboard may look like memory address A3F2H.
To get what key is being pressed, the microprocessor simply reads
the data at location A3F2H.
– The communication process between the microprocessor
and peripheral devices consist of the following three steps:
– Identify the address.
– Transfer the binary information.
– Provide the right timing signals.
10

The Read Operation
– To read the contents of a memory location, the
following steps take place:
• The microprocessor places the 16-bit address of the
memory location on the address bus.
• The microprocessor activates a control signal called
“memory read” which enables the memory chip.
• The memory decodes the address and identifies the
right location.
• The memory places the contents on the data bus.
• The microprocessor reads the value of the data bus
after a certain amount of time.
11

Internal Data Operations
• The 8085 can perform a number of internal
operations. Such as: storing data, Arithmetic &
Logic operations, Testing for condition, etc.
– To perform these operations, the microprocessor
needs an internal architecture similar to the
following:
12
Accumulator Flags
B C
D E
H L
Program Counter
Stack Pointer
Data
Address 8
16

• Registers
Six general purpose registers used to store 8-bit data
during a program execution
The registers are identified as B, C, D, E, H, and L
They can be combined as register pairs: BC, DE, and HL to
perform 16-bit operations
• Accumulator
8-bit register that is part of the ALU
Used to store 8-bit data and in performing 8-bit
arithmetic and logical operations, and in storing the
results op operations
13

The Internal Architecture
• The Program Counter (PC)
– This is a register that is used to control the
sequencing of the execution of instructions.
– This register always holds the address of the next
instruction.
– Since it holds an address, it must be 16 bits wide.
14

The Internal Architecture
• The Stack pointer
– The stack pointer is also a 16-bit register that is
used to point into memory.
– The memory this register points to is a special
area called the stack.
– The stack is an area of memory used to hold data
that will be retreived soon.
– The stack is usually accessed in a Last In First Out
(LIFO) fashion.
15

Externally-Initiated Operations
• External devices can initiate (start) one of the 4
following operations:
– Reset
• All operations are stopped and the program counter is reset
to 0000.
– Interrupt
• The microprocessor’s operations are interrupted and the
microprocessor executes what is called a “service routine”.
• This routine “handles” the interrupt, (perform the necessary
operations). Then the microprocessor returns to its previous
operations and continues.
16

Externally-Initiated Operations
– Ready
• The 8085 has a pin called RDY. This pin is used by external
devices to stop the 8085 until they catch up.
• As long as the RDY pin is low, the 8085 will be in a wait state.
– Hold
• The 8085 has a pin called HOLD. This pin is used by external
devices to gain control of the busses.
• When the HOLD signal is activated by an external device, the
8085 stops executing instructions and stops using the
busses.
• This would allow external devices to control the information
on the busses. Example DMA.
17

8085 Pin Configuraation
• 40 Pins.
• Address Bus A15 – A8 (8 Pins)
• Data Bus AD7 – AD0 (8 Pins)
• Control and Status Signals (6 Pins)
• Power supply and clock frequency (5 Pins)
• Externally initiated signals (11 Pins)
• Serial I/O Ports (2 Pins)
18

Addressing Modes
• Immediate
• Direct
• Indirect
• Register
• Register Indirect
• Displacement (Indexed)
• Stack
20

Immediate Addressing
• Operand is part of instruction
• Operand = address field
• e.g. ADD 5
– Add 5 to contents of accumulator
– 5 is operand
• No memory reference to fetch data
• Fast
• Limited range
21

Immediate Addressing Diagram
Operand
Opcode
Instruction
22

Direct Addressing
• Address field contains address of operand
• Effective address (EA) = address field (A)
• e.g. ADD A
– Add contents of cell A to accumulator
– Look in memory at address A for operand
• Single memory reference to access data
• No additional calculations to work out
effective address
• Limited address space 23

Direct Addressing Diagram
Address A
Opcode
Instruction
Memory
Operand
24

Indirect Addressing (1)
• Memory cell pointed to by address field
contains the address of (pointer to) the
operand
• EA = (A)
– Look in A, find address (A) and look there for
operand
• e.g. ADD (A)
– Add contents of cell pointed to by contents of A to
accumulator
25

Indirect Addressing (2)
• Large address space
• 2n where n = word length
• May be nested, multilevel, cascaded
– e.g. EA = (((A)))
• Draw the diagram yourself
• Multiple memory accesses to find operand
• Hence slower
26

Indirect Addressing Diagram
Address A
Opcode
Instruction
Memory
Operand
Pointer to operand
27

Register Addressing (1)
• Operand is held in register named in address
filed
• EA = R
• Limited number of registers
• Very small address field needed
– Shorter instructions
– Faster instruction fetch
28

Register Addressing (2)
• No memory access
• Very fast execution
• Very limited address space
• Multiple registers helps performance
– Requires good assembly programming or compiler
writing
– N.B. C programming
• register int a;
• c.f. Direct addressing
29

Register Addressing Diagram
Register Address R
Opcode
Instruction
Registers
Operand
30

Register Indirect Addressing
• C.f. indirect addressing
• EA = (R)
• Operand is in memory cell pointed to by
contents of register R
• Large address space (2n)
• One fewer memory access than indirect
addressing
31

Register Indirect Addressing Diagram
Register Address R
Opcode
Instruction
Memory
Operand
Pointer to Operand
Registers
32

Bit position of different flag register
33

Instruction Set of 8085
 An instruction is a binary pattern designed inside a
microprocessor to perform a specific function.
 The entire group of instructions that a microprocessor
supports is called Instruction Set.
 8085 has 246 instructions.
 Each instruction is represented by an 8-bit binary value.
 These 8-bits of binary value is called Op-Code or
Instruction Byte.
37

Classification of Instruction Set
• Data Transfer Instruction
• Arithmetic Instructions
• Logical Instructions
• Branching Instructions
• Control Instructions
38

Data Transfer Instructions
• These instructions move data between
registers, or between memory and registers.
• These instructions copy data from source to
destination.
• While copying, the contents of source are not
modified.
39

Opcode Operand Description
MOV Rd, Rs
M, Rs
Rd, M
Copy from source to destination.
 This instruction copies the contents of the source register into
the destination register.
 The contents of the source register are not altered.
 If one of the operands is a memory location, its location is
specified by the contents of the HL registers.
 Example: MOV B, C or MOV B, M
40

MVI Rd, Data
M, Data
Move immediate 8-bit
 The 8-bit data is stored in the destination register or
memory.
 If the operand is a memory location, its location is
specified by the contents of the H-L registers.
 Example: MVI B, 57H or MVI M, 57H
41

LDA 16-bit address Load Accumulator
 The contents of a memory location, specified by a
16-bit address in the operand, are copied to the
accumulator.
 The contents of the source are not altered.
 Example: LDA 2034H
42

LDAX B/D Register Pair Load accumulator indirect
 The contents of the designated register pair point to a memory
location.
 This instruction copies the contents of that memory location into
the accumulator.
 The contents of either the register pair or the memory location are
not altered.
 Example: LDAX B
43

LXI Reg. pair, 16-bit
data
Load register pair immediate
 This instruction loads 16-bit data in the register pair.
 Example: LXI H, 2034 H
44

LHLD 16-bit address Load H-L registers direct
 This instruction copies the contents of memory
location pointed out by 16-bit address into register L.
 It copies the contents of next memory location into
register H.
 Example: LHLD 2040 H
45

STA 16-bit address Store accumulator direct
 The contents of accumulator are copied into the
memory location specified by the operand.
 Example: STA 2500 H
46

STAX Reg. pair Store accumulator indirect
 The contents of accumulator are copied into the
memory location specified by the contents of the
register pair.
 Example: STAX B
47

SHLD 16-bit address Store H-L registers direct
 The contents of register L are stored into memory
location specified by the 16-bit address.
 The contents of register H are stored into the next
memory location.
 Example: SHLD 2550 H
48

XCHG None Exchange H-L with D-E
 The contents of register H are exchanged with the
contents of register D.
 The contents of register L are exchanged with the
contents of register E.
 Example: XCHG
49

SPHL None Copy H-L pair to the Stack Pointer (SP)
 This instruction loads the contents of H-L pair into
SP.
 Example: SPHL
50

XTHL None Exchange H–L with top of stack
 The contents of L register are exchanged with the
location pointed out by the contents of the SP.
 The contents of H register are exchanged with the
next location (SP + 1).
 Example: XTHL
51

PCHL None Load program counter with H-L contents
 The contents of registers H and L are copied into the
program counter (PC).
 The contents of H are placed as the high-order byte
and the contents of L as the low-order byte.
 Example: PCHL
52

PUSH Reg. pair Push register pair onto stack
 The contents of register pair are copied onto stack.
 SP is decremented and the contents of high-order registers (B,
D, H, A) are copied into stack.
 SP is again decremented and the contents of low-order
registers (C, E, L, Flags) are copied into stack.
 Example: PUSH B
53

POP Reg. pair Pop stack to register pair
 The contents of top of stack are copied into register pair.
 The contents of location pointed out by SP are copied to the
low-order register (C, E, L, Flags).
 SP is incremented and the contents of location are copied to
the high-order register (B, D, H, A).
 Example: POP H
54

OUT 8-bit port address Copy data from accumulator to a port with 8-bit
address
 The contents of accumulator are copied into the I/O
port.
 Example: OUT 78 H
55

IN 8-bit port address Copy data to accumulator from a port with 8-bit
address
 The contents of I/O port are copied into accumulator.
 Example: IN 8C H
56

Arithmetic Instructions
• These instructions perform the operations
like:
– Addition
– Subtract
– Increment
– Decrement
57

Addition
• Any 8-bit number, or the contents of register,
or the contents of memory location can be
added to the contents of accumulator.
• The result (sum) is stored in the accumulator.
• No two other 8-bit registers can be added
directly.
• Example: The contents of register B cannot be
added directly to the contents of register C.
58

Subtraction
• Any 8-bit number, or the contents of register, or the
contents of memory location can be subtracted from
the contents of accumulator.
• The result is stored in the accumulator.
• Subtraction is performed in 2’s complement form.
• If the result is negative, it is stored in 2’s complement
form.
• No two other 8-bit registers can be subtracted directly.
59

Increment / Decrement
• The 8-bit contents of a register or a memory
location can be incremented or decremented
by 1.
• The 16-bit contents of a register pair can be
incremented or decremented by 1.
• Increment or decrement can be performed on
any register or a memory location.
60

ADD R
M
Add register or memory to accumulator
 The contents of register or memory are added to the contents of
accumulator.
 The result is stored in accumulator.
 If the operand is memory location, its address is specified by H-L pair.
 All flags are modified to reflect the result of the addition.
 Example: ADD B or ADD M
61

ADC R
M
Add register or memory to accumulator with
carry
 The contents of register or memory and Carry Flag (CY) are added to the
contents of accumulator.
 Example: ADC B or ADC M
62

ADI 8-bit data Add immediate to accumulator
 The 8-bit data is added to the contents of
accumulator.
 All flags are modified to reflect the result of the
addition.
 Example: ADI 45 H 63

ACI 8-bit data Add immediate to accumulator with carry
 The 8-bit data and the Carry Flag (CY) are added to the
contents of accumulator.
 Example: ACI 45 H
64

DAD Reg. pair Add register pair to H-L pair
 The 16-bit contents of the register pair are added to the
contents of H-L pair.
 The result is stored in H-L pair.
 If the result is larger than 16 bits, then CY is set.
 No other flags are changed.
 Example: DAD B
65

SUB R
M
Subtract register or memory from accumulator
 The contents of the register or memory location are subtracted from the
contents of the accumulator.
 All flags are modified to reflect the result of subtraction.
 Example: SUB B or SUB M
66

SBB R
M
Subtract register or memory from accumulator
with borrow
 The contents of the register or memory location and Borrow Flag (i.e. CY)
are subtracted from the contents of the accumulator.
 Example: SBB B or SBB M
67

SUI 8-bit data Subtract immediate from accumulator
 The 8-bit data is subtracted from the contents of the
accumulator.
 Example: SUI 45 H
68

SBI 8-bit data Subtract immediate from accumulator with
borrow
 The 8-bit data and the Borrow Flag (i.e. CY) is subtracted
from the contents of the accumulator.
 Example: SBI 45 H
69

INR R
M
Increment register or memory by 1
 The contents of register or memory location are incremented
by 1.
 The result is stored in the same place.
 If the operand is a memory location, its address is specified by
the contents of H-L pair.
 Example: INR B or INR M
70

INX R Increment register pair by 1
 The contents of register pair are incremented by 1.
 Example: INX H
71

DCR R
M
Decrement register or memory by 1
 The contents of register or memory location are decremented
by 1.
 If the operand is a memory location, its address is specified by
the contents of H-L pair.
 Example: DCR B or DCR M
72

DCX R Decrement register pair by 1
 The contents of register pair are decremented by 1.
 Example: DCX H
73

Logical Instructions
• These instructions perform logical operations on data
stored in registers, memory and status flags.
• The logical operations are:
– AND
– OR
– XOR
– Rotate
– Compare
– Complement
74

AND, OR, XOR
• Any 8-bit data, or the contents of register, or
memory location can logically have
– AND operation
– OR operation
– XOR operation
with the contents of accumulator.
• The result is stored in accumulator.
75

Rotate
• Each bit in the accumulator can be shifted
either left or right to the next position.
76

Compare
• Any 8-bit data, or the contents of register, or
memory location can be compares for:
– Equality
– Greater Than
– Less Than
with the contents of accumulator.
• The result is reflected in status flags.
77

Complement
• The contents of accumulator can be
complemented.
• Each 0 is replaced by 1 and each 1 is replaced
by 0.
78

CMP R
M
Compare register or memory with accumulator
 The contents of the operand (register or memory)
are compared with the contents of the accumulator.
 Both contents are preserved .
 The result of the comparison is shown by setting the
flags of the PSW as follows:
79

CMP R
M
Compare register or memory with accumulator
 if (A) < (reg/mem): carry flag is set
 if (A) = (reg/mem): zero flag is set
 if (A) > (reg/mem): carry and zero flags are reset.
 Example: CMP B or CMP M
80

CPI 8-bit data Compare immediate with accumulator
 The 8-bit data is compared with the contents of
accumulator.
 The values being compared remain unchanged.
 The result of the comparison is shown by setting the
flags of the PSW as follows:
81

CPI 8-bit data Compare immediate with accumulator
 if (A) < data: carry flag is set
 if (A) = data: zero flag is set
 if (A) > data: carry and zero flags are reset
 Example: CPI 89H
82

ANA R
M
Logical AND register or memory with
accumulator
 The contents of the accumulator are logically ANDed with the contents of
register or memory.
 The result is placed in the accumulator.
 If the operand is a memory location, its address is specified by the contents
of H-L pair.
 S, Z, P are modified to reflect the result of the operation.
 CY is reset and AC is set.
 Example: ANA B or ANA M.
83

ANI 8-bit data Logical AND immediate with accumulator
 The contents of the accumulator are logically ANDed with the
8-bit data.
 S, Z, P are modified to reflect the result.
 CY is reset, AC is set.
 Example: ANI 86H.
84

XRA R
M
Exclusive OR register or memory with
accumulator
 The contents of the accumulator are XORed with the contents of the register or memory.
 If the operand is a memory location, its address is specified by the contents of H-L pair.
 CY and AC are reset.
 Example: XRA B or XRA M.
85

ORA R
M
Logical OR register or memory with accumulator
 The contents of the accumulator are logically ORed with the contents of the register or
memory.
 If the operand is a memory location, its address is specified by the contents of H-L pair.
 Example: ORA B or ORA M.
86

ORI 8-bit data Logical OR immediate with accumulator
 The contents of the accumulator are logically ORed with the 8-
bit data.
 Example: ORI 86H.
87

XRA R
M
Logical XOR register or memory with
accumulator
 The contents of the accumulator are XORed with the contents of the
register or memory.
 If the operand is a memory location, its address is specified by the
contents of H-L pair.
 Example: XRA B or XRA M.
88

Branching Instructions
• The branching instruction alter the normal
sequential flow.
• These instructions alter either unconditionally
or conditionally.
89

Control Instructions
• The control instructions control the operation
of microprocessor.
90

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