Undergraduate course content: Introduction to microprocessors, The 8086 microprocessor architecture: Microprocessor ALSU functions Microprocessor 8 bits bus architecture Microprocessor 8/16 bits bus architecture 8086/8088 microprocessor registers 8086/8088 microprocessor instruction set RISC and CISC architectures External memory Tracing Program Codes Application Examples 8086 Interrupts Interrupt priority controller Microprocessor-based data communication

1. Microprocessor-Based Systems
Dr. Randa Elanwar
Lecture 1

2. Lecture Content
• Introduction to microprocessors,
• Comparison of typical microprocessors
• The 8086 microprocessor architecture:
– The microprocessor system: CPU, memory, I/O
– The microprocessor Pin outs, clock circuitry,
– Bus structure: address bus, data bus, and control bus
connections
– The microprocessor instruction sets
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3. Introduction to microprocessors
• Definition: Microprocessor
• Is a digital integrated circuit(s) capable of executing
program
• Definition: Program
• Is a set of instructions to be executed in sequence
• Definition: Central processing unit (CPU)
• Is a logic circuit controlling the operation of the computer
• Microprocessors perform the function of a CPU in micro-
computer systems.
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4. Introduction to microprocessors
• Microprocessors started at mid 70’s
• The data/information processed by a microprocessor
(electronic circuits) is usually represented in binary format.
• Each binary digit represent a power of 2. A binary digit is
often called a ‘bit’
• The binary system uses only two symbols zero (0) and one (1)
• Binary numbers are often called ‘binary words’.
• A 4-bit binary word is called a ‘nibble’.
• An 8-bit binary word is called a ‘byte’.
• A 16-bit binary word is called a ‘word’.
• A 32-bit binary word is called a ‘long word’/‘double word’.
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5. Introduction to microprocessors
• Binary information is fed to the electronic circuits by voltage
levels.
• Standard logic circuits use 5 volts power supply.
• Low voltage circuits use 3 volts power supply, thus consumes
less power as in portable computers.
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•Binary information is =1 if 3v <= voltage
<= 5v, and information is =0 if 0v <=
voltage <= 1v
•If 1v < voltage < 3v, the binary
information level is considered undefined. Low
High
Undefined
0 v
1 v
3 v
5 v

6. Introduction to microprocessors
• The simple microprocessor major parts are: The
central processing unit (CPU), memory, and the
input/output circuitry.
• Connecting these three parts are three sets of
parallel lines called buses. The three buses are the
address bus, the data bus and the control bus.
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7. Introduction to microprocessors
The Central Processing Unit (CPU)
• The CPU controls the operation of the computer.
• The CPU fetches binary coded instructions from memory,
decodes the instructions into simple actions and carries out
these actions in sequence of steps.
• The CPU also contains an “address counter”, which holds the
address of the next instruction or data item to be fetched
from memory or temporary storage registers.
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8. Introduction to microprocessors
Memory
• Memory has 2 purposes: store the binary codes of
instructions to be carried out and store the binary coded data
with which the computer is going to be working.
• Memory types are either ROMs or RAMs. These are
implemented using logical gates circuitry (e.g. D flip flops)
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Clock
+ -
Clock
(CLK)

9. Introduction to microprocessors
• If the flip flop is +ve edge sensitive, the output (Q) will be equal
to the input (D) only at the +ve edge of the clock (active high)
• If the flip flop is -ve edge sensitive, the output (Q) will be equal
to the input (D) only at the -ve edge of the clock (active low)
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10. Introduction to microprocessors
• Example (active high)
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Input
Output
CLK

11. Introduction to microprocessors
• Inputs and Outputs (I/O)
• The I/O section allows the computer to take in data or send out
data.
• Peripherals such as keyboards, monitors, printers and modems
are connected to the I/O section through ports.
• The simplest type of input or output port is just a set of parallel
D flip-flops (Register)
Example: 8 bit register
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12. Introduction to microprocessors
• Inputs and Outputs (I/O)
• In the 8 bit register we have 1 pin for GND, 8 pins for inputs, 8
pins for outputs, 1 for clock and 2 for supply (20 pins)
• For an input port, the D inputs will be connected to the external
device and the Q outputs will be connected to the data bus
which runs to the CPU.
• For an output port, the D inputs will be connected to the data
bus which runs to the CPU and the Q outputs will be connected
to the external device.
• In either cases the data is transferred to/from the bus is enabled
only when receiving a control signal from the CPU (usually the
clock)
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13. Introduction to microprocessors
• Example:
• It is not a must that the data stored in register A is the same
stored in register B because this depends on their clocks.
• In most cases a master clock only is available thus we need
another control signal such that data goes to/from the
intended registers only (chip selection CS)
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Reg A Reg B
8 input lines
CLKA CLKB

14. Introduction to microprocessors
• Example: to transfer data from Reg A to Reg B
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Reg A Reg B
8 input lines
CLKA CLKB
CSA CSB
CSA
CLKB

15. Introduction to microprocessors
• The address bus
• It consists of 16, 20, 24, 32 parallel signal lines. On these lines
the CPU sends out the address of the memory location that is to
be written to or read from.
• The number of memory locations that the CPU can address is
determined by the bus size.
• If the CPU has N address lines it can address 2N memory
locations.
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# Address lines # Memory locations
16 65,536
20 1,048,576
24 16,777,216

16. Introduction to microprocessors
• The data bus
• It consists of 8, 16 or 32 parallel signal lines. They are
bidirectional lines.
• The CPU can read data from memory/port and write data to
memory/port on these lines.
• Many devices have their outputs connected to the data bus
thus they must have a selection signal.
• The control bus
• It consists of 4 to 10 parallel signal lines.
• The CPU sends out signals on the control bus to enable the
outputs of addressed memory or port devices.
• Typical control bus signals are Memory Read, Memory Write,
I/O Read and I/O Write.
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17. Introduction to microprocessors
• Example: Memory Read
• To read a byte of data from a memory location, the CPU sends out
the memory address of the desired byte on the address bus and
then sends out a Memory Read signal on the control bus.
• The Memory Read signal enables the addressed memory device to
output a data word onto the data bus.
• The data word from memory travels along the data bus to the
CPU.
• Example: 3 Instructions program
1. Input a value from a keyboard connected to the port at address
05H
2. Add 7 to the value read in
3. Output the result to a display connected to the port at address
02H
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18. Introduction to microprocessors
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19. Comparison of typical microprocessors
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8086 8088
16 bit microprocessor,
16 bit data bus, 20 bit
address bus
16 bit
microprocessor, 8 bit
data bus, 20 bit
address bus
The arithmetic logic
unit has internal
registers
Same as 8086
Instructions work with
16 bit binary words
Same as 8086
Read/write data either
8 or 16 bit at a time
Read/write data
either 8 bits at a
time
Can address 220
memory locations
Can address 220
memory locations
Reads 16 bit word in 1
operation
Reads 16 bit word in
2 operations
The 80186 is an improved version of
8086 and 80188 is an improved version
of 8088 with instruction set that is a
superset of the instruction set of the
8086. Both are 16 bit microprocessors.
The 80286 is a 16 bit microprocessor
advanced version of the 8086 designed
for multitasking microcomputers.
The 80386 is a 32 bit microprocessor
which can address up to 4 gigabytes
memory used in multitasking
microcomputers.
Self study: you can read more about the
competitive microprocessors and find
out the aspects of comparison

20. Microprocessor bus architecture and
instruction sets
• Before we talk about how to write a program for the 8086 we
first have to discuss its internal features: ALU, flags, registers,
instruction byte queue and segment registers.
• The 8086 CPU is divided into 2 independent functional parts:
1. Bus interface unit (BIU): sends out addresses, fetches
instructions from memory, reads/writes data from/to ports
and memory
2. Execution unit (EU): tells the BIU where to fetch the
instructions and data from, decodes and execute
instructions
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21. Microprocessor bus architecture and
instruction sets
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To understand this
architecture and
function of each
component we will
have to discuss
several simpler
structures

22. Microprocessor bus architecture and
instruction sets
• Example 1: Simple bus architecture
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Reg A Reg BCLKA CLKB
CSA CSB
Reg C
Reg D
CLKC CLKD
CSC CSD
CLRD
Reg E
CLKE
CSE
CNT Up
CNT DN
•In this architecture we have 3 registers with CS signal (A, B and C)
•Reg D has an active low CLR signal
•Reg E has two active low signal (CNT UP) to increment its contents by 1 at
every –ve edge and (CNT DN) to decrement its contents by 1 at every –ve
edge
•We will discuss how this architecture executes these simple instructions:
MOV B, A CLR A INC B

23. Microprocessor bus architecture and
instruction sets
23Microprocessor-Based Systems Dr. Randa Elanwar
CSA
CLKB
MOV B, A:
means move the content of A to B
We select Reg A to output data on bus
We activate Reg B clock to read the data on bus
CLR A:
Reg A doesn’t have a CLR signal input
Use Reg D to clear its content
move this content to Reg A (MOV A, D)
CSD
CLKA
CLRD
PD
PD
CSB
CLKE
CSE
CLKB
CNT UP
INC B:
Reg B doesn’t have a CNT UP signal input
move this content to Reg E (MOV A, E)
Use Reg E to increment its content
move this content to Reg B (MOV B, E)
PD: propagation delay

24. Microprocessor bus architecture and
instruction sets
• Example 2: Advanced bus architecture
24Microprocessor-Based Systems Dr. Randa Elanwar
Reg A
CLKA
CSA Reg B
CLKB
CSB
Reg C
CLKC
CSC
Reg D
CLKD
CSD
Reg E
CLKE
CSE
CLKT
T1
CF
CSALU
Xin
Yin
Z
ALSU
mode
In this architecture: Reg A
is known as “Accumulator”
i.e. accumulate results of
ALSU

25. Microprocessor bus architecture and
instruction sets
• Example 2: Advanced bus architecture
25Microprocessor-Based Systems Dr. Randa Elanwar
Reg A
CLKA
CSA Reg B
CLKB
CSB
Reg C
CLKC
CSC
Reg D
CLKD
CSD
Reg E
CLKE
CSE
CLKT
T1
CF
CSALU
Xin
Yin
Z
ALSU
mode
The buffer is used to isolate
the output of Reg A if CSA is
low and as a 8 bit buffer if
CSA is high

26. Microprocessor bus architecture and
instruction sets
• Example 2: Advanced bus architecture
26Microprocessor-Based Systems Dr. Randa Elanwar
Reg A
CLKA
CSA Reg B
CLKB
CSB
Reg C
CLKC
CSC
Reg D
CLKD
CSD
Reg E
CLKE
CSE
CLKT
T1
CF
CSALU
Xin
Yin
Z
ALSU
mode
T1 is a temporary
register. Takes the input
only from the bus and
outputs its content as
ALSU Yin. Doesn’t have
to be isolated,  has
no CS control line

27. Microprocessor bus architecture and
instruction sets
• Example 2: Advanced bus architecture
27Microprocessor-Based Systems Dr. Randa Elanwar
Reg A
CLKA
CSA Reg B
CLKB
CSB
Reg C
CLKC
CSC
Reg D
CLKD
CSD
Reg E
CLKE
CSE
CLKT
T1
CF
CSALU
Xin
Yin
Z
ALSU
mode
ALSU: Arithmetic Logic
Shift Unit. It does
binary/decimal
arithmetic operations (+,-
,*,/), logic operations
(>,=,<,complement) and
shift operations

28. Microprocessor bus architecture and
instruction sets
• Example 2: Advanced bus architecture
28Microprocessor-Based Systems Dr. Randa Elanwar
Reg A
CLKA
CSA Reg B
CLKB
CSB
Reg C
CLKC
CSC
Reg D
CLKD
CSD
Reg E
CLKE
CSE
CLKT
T1
CF
CSALU
Xin
Yin
Z
ALSU
mode
If we want to add A and B:
ADD A, B
Means A+BA
The micro-operations will be:
1. Move B to T1
2. Select ALSU addition Mode
3. Set CSALSU low (result Z is on the
bus)
4. Set CLKA low to move (A takes
the result)

29. Microprocessor bus architecture and
instruction sets
• Example 2: Advanced bus architecture
29Microprocessor-Based Systems Dr. Randa Elanwar
Reg A
CLKA
CSA Reg B
CLKB
CSB
Reg C
CLKC
CSC
Reg D
CLKD
CSD
Reg E
CLKE
CSE
CLKT
T1
CF
CSALU
Xin
Yin
Z
ALSU
mode
CF: Carry flag, a flip flop that holds
the carry for arithmetic operations
To avoid racing (continuous
addition, we introduce time delay
between input A (Xin) and output A
(Z) using a master-slave flip flop
To add Reg B and C for example we
need a new architecture

30. Microprocessor bus architecture and
instruction sets
• Example 3: Advanced bus architecture
30Microprocessor-Based Systems Dr. Randa Elanwar
T2
CLKT2
Reg A
CLKA
CSA
Reg B
CLKB
CSB
Reg C
CLKC
CSC
Reg D
CLKD
CSD
CLKT1
T1
CF
CSALU
Xin
Yin
Z
ALSU
mode
Now if we want to add B and C and
store the result in D
The micro-operations will be:
1. Move B to T1
2. Move C to T2
3. Select ALSU addition Mode
4. Set CSALSU low (result Z is on the
bus)
5. Set CLKD low to move (D takes
the result)

31. Microprocessor bus architecture and
instruction sets
• Example 3: Advanced bus architecture
31Microprocessor-Based Systems Dr. Randa Elanwar
T2
CLKT2
Reg A
CLKA
CSA
Reg B
CLKB
CSB
Reg C
CLKC
CSC
Reg D
CLKD
CSD
CLKT1
T1
CF
CSALU
Xin
Yin
Z
ALSU
mode
Thus structure enables the addition
of 1 byte to 1 byte
Ex: 0011 1010
+
1011 1100
1111 0110
cc c
Multi-byte addition needs store the
carry in a D flip flop  Carry flag