Microprocessor design and Lecture One.pptx

Sept to Dec 2022 Wednesday, January 22, 2025
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MICROPROCESSOR
SYSTEMS DESIGN
COMP 413

Wednesday, January 22, 2025
Sept to Dec 2022
2
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 At the end of this course Comp 413 you should be
able to;
 Discuss the basic function a microprocessor in any system
 Describe the benefits that microprocessor controlled
designs have over hard-wired IC logic designs,
 Discuss the functional blocks of a microprocessor-based
system having basic input/output capability
 Describe the function of the address, data, and control bus
 Describe the flow of data through the Internal parts of an
8085 microprocessor

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Cont.,
 Discuss the function of the I/O ports in any microprocessor
controlled system
 Design and implement a microprocessor/microcontroller
controlled system

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Introduction
 Design applications previously studied involved
Combinational and Sequential logic ICs (Comp 211 & Comp
312).
 Combinational circuits;circuits realized by combination of
logic gates(AND,OR,NOT etc)
 Sequential circuits;combinational logic circuits with memory
 A complete design could be within the realm of Small Scale
Integration (SSI) and Medium Scale Integration (MSI)
 An example is that of a traffic light controller that goes through
the sequence; green-yellow-red.
 To implement this logic , some counter ICs are used for timing, shift register
ICs for sequencing the lights, and a D- Flip Flop to interrupt the sequence
with a crosswalk push button for pedestrian crossing

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 When it comes to modern complexity of electronic
controls for example in the modern automobiles,
there exists several analog quantities to monitor
such as;
 engine speed,
 manifold pressure (inlet and exhaust pipes ),
 coolant temperature
 there are also digital control functions to spark plug timing,
fuel mixture control, and radiator circulation control.
 It means therefore that there are calculations and
decision making continuously taking place. This
therefore makes it an application for a
microprocessor.

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 A microprocessor based design is therefore
convenient whenever an application involves;
 Making calculations
 Making decisions based on external stimulus
 Maintaining memory of past events

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 A microprocessor therefore has more advantages
over the hard-wired SSI/MSI IC approach;
 It is a general purpose device
 Performs any function depending on the control
program
 Making changes is done by changing instructions in
the program. Hard-wired will be redesigned and
reconstructed
 New microprocessors come to the market every
year to meet needs of designers, however the
theory behind this technology remains basically the
same.

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 A microprocessor is a general purpose device that
is driven by software instructions and communicates
with several external support chips to perform
input/output of a specific task.
 A microprocessor is also referred to as a CPU
 This course will be based on the 8085
microprocessor that runs at a frequency of either
3.03MHZ(8085A) or 5MHZ maximum(8085A-2).
 16 bit address and 8 bit data bus

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An 8085A Microprocessor

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Pin Arrangement
 The pins on the chip can be grouped into six groups:
 Address Bus
 Data Bus
 Power supply and clock signals
 Serial I/O ports(SID,SOD)
 Control and Status signals
 Externally initiated signals

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Address and Data Bus(lines)
 Address bus has 8 lines A8 – A15 which are unidirectional.
The remaining 8 bits address are multiplexed (time shared)
with the 8 data bit lines.
 AD0 – AD7 serve both as bi-directional data bus D0 – D7 and
A0 – A7 for address lines to make 16-bits with A8 – A15
 During the execution of the instruction, the lines will carry
the address bits and during execution will carry the 8 bit data.
 Addresses originate from the microprocessor and so are
unidirectional and data lines are bidirectional since data
flows in and out of the processor.

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Cont.
 Latches can be used to save/hold the information
before the function of the bits change.

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Clock signals
 X1 and X2 are the inputs from the crystal oscillator or
clock generating circuit.
 Clk out pin: An output clocking pin to drive the rest
of the system.

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Control and Status signals
 ALE: Address Latch Enable. Set to 1 by the
system when AD0 – AD7 lines have an address on
them. It changes back to 0 thereafter. This signal can
be used to save the address bits from the AD lines.
 RD: Read. Active Low signal to enable a read from
a memory location.
 WR: Write. Active Low signal to enable a write to a
memory location.

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Cont.
 IO/M:Input,Output/Memory. This signal specifies
whether the operation is a memory operation(IO/M
= 0) or an I/O operation (IO/M =1).
 S1 and S2 : Status signals to specify the kind of
operation being performed.

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Fetching an Instruction
 Assume the processor is fetching an instruction from
address 8400H. That means the Program
Counter(PC) is loaded with this value.
 The PC places the address value on the address bus and the
controller issues a RD signal.
 The memory’s address decoder gets the value and determines
which memory location is being accessed.

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Cont.
 The value on the memory location is placed on the
data bus.
 The value on the data bus is read into the Instruction
Register(IR) inside the microprocessor.
 Then transferred to the Instruction Decoder(ID)
inside the microprocessor for decoding.
 After decoding the instruction, the control unit
issues control signals to perform the operation.

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 All instruction would go through Fetch, Decode , and
Execution cycle

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8085 Features
 The ALU
 In addition to the arithmetic & Logic circuits, the ALU includes
the accumulator, which is part of every arithmetic and logic
operation.
 The ALU also includes a temporary register that is used for
temporary data storage during the execution of an operation.
The temporary register is not accessible by the programmer.

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Cont.
 The Flag Register(program status word)
 The flag register consists of five status flags
 The sign flag(S): This is set to the value of the most significant
bit of the accumulator after an arithmetic or logic operation (0
for positive and 1 for negative).
 The zero flag(Z) is set to a 1 whenever an arithmetic or logic
operation produces a result of zero. A nonzero result sets it to 0.

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Cont.
 The auxiliary carry flag(Ac): Reflects any carry from bit 3 to
bit 4(assuming an 8-bit data with bit 0 as the LSB and bit 7 as the
MSB).
 The parity status flag(P): is set to 1 if an operation produces an
answer with even parity.
 The carry flag(Cy): Reflects the final carry out of the most
significant bit of any arithmetic operation. The flag is also used for
the shift and rotate instructions.

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Register Structure
The Accumulator:
 The accumulator(A) is an 8-bit register.
 Most arithmetic and logic operations are performed
using the accumulator.
 All I/O operations are performed via the
accumulator

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Cont.
General purpose registers:
 The B,C,D,E,H and L registers are 8-bits long and
are used for moving data between themselves, the
accumulator and the memory.
 There are a number of instructions that combine two
of these 8-bit registers to form 16-bit register pair.

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Cont.
 Arithmetic operations use B and C, or D and E, or H
and L as 16-bit data registers.
 Register HL is the memory address register or data
counter. The register pair stores the 16-bit address
of an 8-bit data being accessed from memory.

Microprocessor design and Lecture One.pptx

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Microprocessor design and Lecture One.pptx