Chapter 8 Embedded Hardware Design and Development (third portion)

Introduction to
EMBEDDED SYSTEM
(2nd Edition)
SHIBU K V
Dr Moe Moe Myint
Department of Computer Engineering & Information Technology
Mandalay Technological University
www.slideshare.net/MoeMoeMyint
moemoemyint@mtu.edu.mm
drmoemoemyint.blogspot.com
IT-52061
Chapter 8
Embedded Hardware Design and Development

Learning Objectives
 Learn about the various elements of Embedded Hardware and their design principles
 Refresh knowledge on the basic Analog Electronic components and circuits – Resistor, Capacitor, Diode,
Inductor, Transistor etc. and their use in embedded applications
 Refresh knowledge on the basic Digital Electronic components and circuits – Logic Gates, Buffer Ics, Latch
ICs, Decoder and Encoder ICs, Multiplexer (MUX) and De-multiplexer (D-MUX), Combinational and
Sequential Circuits and their use in embedded applications
 Learn about Integrated Circuits (ICs), the degree of integration in various types of Integrated Circuits,
Analog, Digital and Mixed Signal Integrated Circuits, the steps involved in IC Design
Department of Computer Engineering and Information Technology
Lecture Slides for Textbook Introduction to Embedded Systems, Moe Moe Myint, 2017-2018

Outlines
 Analog Electronic Components 229 (Roll no.1)
 Digital Electronic Components 230 (Roll no. 2,3,4,5,6,7,8,9,10,11)
 VLSI and Integrated Circuit Design 243 (Roll no. 12, 13,14)
 Electronic Design Automation (EDA) Tools 248
 How to use the Eagle EDA Tool? 249
 Schematic Design using Eagle Capture CIS 249
 The PCB Layout Design 267
 Printed Circuit Board (PCB) Fabrication 288
3
Finished

LogicGateSimulation

ORLogicGateSimulation

NANDLogicGateSimulation

NORLogicGateSimulation

NOTLogicGateSimulation

Buffer
 A buffer circuit is a logic circuit for amplifying the current or power.
 It increases the driving capability of a logic circuit.
 A tri-state buffer is a buffer with Output Enable control.
 When the Output Enable control is active (Low for Active low enable and High for Active high
enable), the tri-state buffer functions as a buffer.
 If the Output Enable is not active, the output of the buffer remains at high impedance state (Tri-
stated).
 Tri-state buffers are commonly used as drivers for address bus and to select the required device
among multiple devices connected to a shared data bus.
 Tri-state buffers are available as either unidirectional or bi-directional buffers.

Cont’d
 74LS244/74HC244 is an example of unidirectional octal buffer. It contains 8 individual buffers which
are grouped into two. Each buffer group has its own output enable line. Figure illustrates the 74LS244
buffer device.
 IC 74LS245 is an example of bi-directional tri-state buffer. It allows data flow in both directional, one
at a time. The data flow direction can be set by the direction control line. One buffer is allocated for the
data line associated with each direction. Figure illustrates the 74LS245 octal bi-directional buffer.
Figure. 74LS244 Octal Buffer IC
Figure. 74LS245 Octal bidirectional Buffer IC

Decoder
 A decoder is a logic circuit which generates all the possible combinations of the input signals.
 Decoders are named with their input line numbers and the possible combinations of the input as
output.
 Examples are 2 to 4 decoder, 3 to 8 decoder and 4 to 16 decoder.
 The 3 to 8 decoder contains 3 input signal lines and it is possible to have 8 different configurations
with the 3 lines (000 to 111 in the input line corresponds to 0 to 7 in the output line).
 Depending on the input signal, the corresponding output line is asserted. For example, for the input
state 001, the output line 2 is asserted.
Decoders are mainly used for address decoding and chip select signal generation in electronic
circuits and are available as integrated circuits.
74LS138/74AHC138 is an example for 3 to 8 decoder IC. Figure illustrates the 74AHC138 decoder
and the function table for it.

Cont’d
 The decoder output is enabled only when the ‘Output Enable’ signal lines E1, E2 and E3 are at
logic levels 0, 0 and 1 respectively.
 If the output-enable signals are not at the required logic state, all the output lines are forced to the
inactive (High) state.
 The output line corresponding to the input state is asserted ‘Low’ when the ‘Output Enable’ signal
lines are at the required logic state (Here E1=E2=0 and E3=1). The output line can be directly
connected to the chip select pin of a device, if the chip select logic of the device is active low.

Cont’d
Inputs
Output
Enable Select
E1 E2 E3 A2 A1 A0 O0 O1 O2 O3 O4 O5 O6 O7
0 0 1 0 0 0 0 1 1 1 1 1 1 1
0 0 1 0 0 1 1 0 1 1 1 1 1 1
0 0 1 0 1 0 1 1 0 1 1 1 1 1
0 0 1 0 1 1 1 1 1 0 1 1 1 1
0 0 1 1 0 0 1 1 1 1 0 1 1 1
0 0 1 1 0 1 1 1 1 1 1 0 1 1
0 0 1 1 1 0 1 1 1 1 1 1 0 1
0 0 1 1 1 1 1 1 1 1 1 1 1 0

Encoder
 An encoder performs the reverse operation of decoder.
The encoder encodes the corresponding input state to a particular output format.
The binary encoder encodes the input to the corresponding binary format.
Encoders are named with their input line numbers and the encoder output format.
Examples are 4 to 2 encoder, 8 to 3 encoder and 16 to 4 encoder.
The 8 to 3 encoder contains 8 input signal lines and it is possible to generate a 3 bit binary output
corresponding to the input (e.g. inputs 0 to 7 are encoded to binary 111 to 000 in the output lines).
The corresponding output line is asserted in accordance with the input signals.
For example, if the input line 1 is asserted, the output lines A0, A1 and A2 are asserted as 0, 1 and 1
respectively.
Encoders are mainly used for address decoding and chip select signal generating in electronic
circuits and are available as integrated circuits.
74F148/74LS148 is an example of 8 to 3 encoder IC. Figure illustrates the 74F148/74LS148
encoder and the function table for it.

Cont’d
Input Select Output
7 6 5 4 3 2 1 0 E1 GS E0 A2 A1 A0
1 1 1 1 1 1 1 0 0 0 1 1 1 1
1 1 1 1 1 1 0 1 0 0 1 1 1 0
1 1 1 1 1 0 1 1 0 0 1 1 0 1
1 1 1 1 0 1 1 1 0 0 1 1 0 0
1 1 1 0 1 1 1 1 0 0 1 0 1 1
1 1 0 1 1 1 1 1 0 0 1 0 1 0
1 0 1 1 1 1 1 1 0 0 1 0 0 1
0 1 1 1 1 1 1 1 0 0 1 0 0 0

Multiplexer (MUX)
 A multiplexer (MUX) can be considered as a digital switch which contains multiple input lines and
a single output line.
 The inputs of a MUX are said to be multiplexed.
 It is a digital circuit which selects one of the n data inputs and routes it to the output.
 74S151 is an example for 8 to 1 multiplexer IC.
 Figure illustrates the 74S151 multiplexer and the function table for it.
Figure. 8 to 1 multiplexer IC and I/O signal states

De-multiplexer (D-MUX)
 A de-multiplexer performs the reverse operation of multiplexer.
 De-multiplexer switches the input signal to the selected output line among a number of output lines.
 The output line to which the input is to be switched is selected by the output selector control lines.
 The 1 to 2 de-multiplexer, NL7SZ18 is a typical example for 1 to 2 de-multiplexer IC.
 It contains a single input line and two output lines to switch the input line.
 The output switching is controlled by the output selector control.
Figure illustrates the NL7SZ18 de-multiplexer and the function table for it.
 When one output line is selected by the output selector control (S), the other output line remains in
the High impedance state.

Combinational Circuits
 In digital system design, a combinational circuit is a combination of the different logic gates.
 The output of the combinational circuit is dependent only on the present state of the inputs at the
given point of time.
 The combinational circuit do not use any memory.
 Encoders, decoders, multiplexers, de-multiplexers, adder circuits, comparators, multiple input
gates, etc. are examples of digital combinational circuits.
 A combinational circuit can have an n number of inputs and m number of outputs

Sequential Circuits
 Digital logic circuit, whose output at any given point of time depends on both the present and past
inputs, is known as sequential circuits.
 Hence, sequential circuits contain a memory element for holding the previous input states.
 In general, a sequential circuit can be visualized as a combinational circuit with memory elements.
 This type of circuits uses previous input, output, clock and a memory element.
Figure. Visualization of Sequential Circuit

Cont’d
 Flip-flops act as the basic building blocks of sequential circuits.
 Sequential circuits are of two types, namely-synchronous (clocked) sequential circuits and
asynchronous sequential circuits.
 The operation of a synchronous sequential circuit is synchronized to a clock signal, whereas an
asynchronous sequential circuit does not require a clock for operation.
 For an asynchronous sequential circuit, the response depends upon the sequence in which the input
signal changes.

Combinational vs Sequential Logic Circuits
Combinational Logic Circuits Sequential Logic Circuits
Output is a function of the present inputs (Time
Independent Logic).
Output is a function of clock, present inputs and the
previous states of the system.
Do not have the ability to store data (state). Have memory to store the present states that is sent
as control input (enable) for the next operation.
It does not require any feedback. It simply outputs
the input according to the logic designed.
It involves feedback from output to input that is
stored in the memory for the next operation.
Used mainly for Arithmetic and Boolean operations. Used for storing data (and hence used in RAM).
Logic gates are the elementary building blocks. Flip flops (binary storage device) are the elementary
building unit.
Independent of clock and hence does not require
triggering to operate.
Clocked (Triggered for operation with electronic
pulses).
Example: Adder [1+0=1; Dependency only on
present inputs i.e., 1 and 0].
Example: Counter [Previous O/P+1=Current O/P;
Dependency on present input as well as previous
state].

Difference between Synchronous and Asynchronous
Sequential Circuits
Synchronous Sequential Circuit Asynchronous Sequential Circuit
Clocked flip-flops act as the memory element in the
circuit. All flip-flops are clocked to the same clock
signal.
Un-clocked flip-flops or logic gate circuits with
feedback loops act as the memory element in the
circuit.
The output state of the circuit changes only with
clock trigger.
The output state change happens instantaneously
with changes in input state.
The speed of operation depends on the maximum
supported clock frequency.
Faster than synchronous sequential circuits.

Integrated Circuit Design
 An integrated circuit (IC) is a miniaturized form of an electronic circuit containing transistors and
other passive electronic components.
 In an IC, the circuits, required for building the functionality, are built on the surface of a thin silicon
wafer.
 The first integrated circuit was designed in the 1950s.
 Depending on the number of integrated components, the degree of integration within an integrated
circuit (IC) is known as:
 Small-Scale Integration (SSI): Integrates one or two logic gate(s) per IC, e.g. LS7400
 Medium-Scale Integration (MSI): Integrates up to 100 logic gates in an IC. The decade Counter 7490 is an example
for MSI device.
 Large-Scale Integration (LSI): Integrates more than 1000 logic gates in an IC.
 Very Large-Scale Integration (VLSI): Integrates millions of logic gates in an IC. Pentium processor is an example of a
VLSI Device.

Different Types of IC Design
Depending on the type of circuits integrated in the IC, the IC design is categorized as:
 Digital Design: Deals with the design of integrated circuits handling digital signals and data. The
I/O requirement for such an IC is always digital. Microprocessor/microcontroller, memory, etc. are
examples of digital data.
 Analog Design: Deals with the design of integrated circuits handling analog signals and data.
Analog design gives more emphasis to the physics aspects of semiconductor devices such as gain,
power dissipation, resistance, etc. RF IC design, Op-Amp design, voltage regulator IC design, etc.
are examples for Analog IC Design.
 Mixed Signal Design: In today’s world, most of the applications require the co-existence of digital
signals and analog signals for functioning. Mixed signal design involves design of ICs, which
handle both digital and analog signals as well as data. Design of an analog-to-digital converter is an
example for mixed signal IC design.

Various Steps Involved in a HDL Based Design
Figure. The HDL based VLSI Design Process
VHDL or Verilog Description
Functional Simulation
Synthesis
Placement and Routing
Timing Simulation
Area and Timing
Constraints
Technology Library
1234

Objective Questions
1. The logic expression 𝑌 = 𝐴B + A 𝐵 represents the logic gate
(a) AND (b) NAND (c) OR (d) XOR (e) NOR
2. Which of the following is an example for Buffer IC?
(a) 74LS00 (b) 74LS244 (c) 74LS08 (d) 74LS373 (e) None of these
3. Which of the following digital circuits is used for selecting one input from a set of inputs and
connecting it to an output line
(a) Buffer (b) Latch (d) Multiplexer (e) De-Multiplexer
(f) None of these
4. Combinational circuits contain a memory element. State True or False.
(a) True (b) False
5. Half Adder is an example of Sequential circuit. State True or False.
(a) True (b) False

Review Questions
1. Explain the role of de-coders in embedded hardware development. Explain the functioning of the
circuit.
2. What is a combinational circuit? Draw a combinational circuit for embedded application
development.
3. What is sequential circuit? Draw a sequential circuit and explain its functioning.
4. Explain the difference between digital combinational and sequential circuits.
5. Explain the difference between synchronous and asynchronous sequential circuits.
6. What is an Integrated Circuit (IC)? Explain the different types of integrations for ICs. Give an
example for each.
7. Explain the different types of IC design. Give an example for each.
8. Explain the different steps involved in VHDL based IC design.

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Chapter 8 Embedded Hardware Design and Development (third portion)

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