Digital circuit that performs a computation tasks
Controller and datapath
General-purpose: variety of computation tasks
Single-purpose: one particular computation task
Custom single-purpose: non-standard task
A custom single-purpose processor may be
– Fast, small, low power
– But, high NRE, longer time-to-market, less flexible
CMOS transistor on silicon
– The basic electrical component in digital systems
– Acts as an on/off switch
– Voltage at “gate” controls whether current flows from source to drain
– Don’t confuse this “gate” with a logic gate
CMOS transistor implementations
Complementary Metal Oxide Semiconductor
We refer to logic levels
– Typically 0 is 0V, 1 is 5V
Two basic CMOS types
– nMOS conducts if gate=1
– pMOS conducts if gate=0
– Hence “complementary”
– Inverter, NAND, NOR
A combinational circuit is a digital circuit whose output is purely a
function of its current inputs;
such a circuit has no memory of past inputs.
Sequential Logic Design
• Define system functionality
• Convert functionality to physical implementation while
• Satisfying constrained metrics
• Optimizing other design metrics
• Designing embedded systems is hard
• Complex functionality
• Millions of possible environment scenarios
• Given this implementation model
– Sequential logic design quickly reduces to combinational logic design
Survey and Reading by students (18 mins.)
Define custom single purpose processors.
Mention the components of combinational logic.
Mention the components of sequential logic.
List out the steps involved in creating a data path.
List out the steps in creating a controller.
1. What are the steps in creating FSM?
2. List out the basic logic gates?
Guided Reading with hints
Page No.: 68-74
Summary (5 mins.)
Custom single-purpose processors
– Combinational logic
– Sequential logic
• Sequential components
• Creating data path and controller
• CMOS transistor on silicon
Straightforward design techniques
Can be built to execute algorithms
Typically start with FSMD
Optimizing Single purpose processors
CAD tools can be of great assistance
Assessment (MCQ And higher order
1. Basic logic gates _________.
2. Drivers ,Inverters are __________ .
(a) OR and XOR
(b) AND and NOT
(c) XOR and XNOR
(d) OR and AND
3. CMOS stands for ___________ .
(a) Complementary Metal Oxide Semiconductor
(b) Complementary Metal Oxide Stub
(c) Complementary Metal Oxide Semi transistor
4. A multiplexer is sometimes called as
5. The components of combinational logic is ______________
(d) All the above
Two mark Questions:
State the benefits of custom single purpose processors.
Mention some of the combinational logic gates.
Define combinational logic design.
Mention the advantages and disadvantages in CMOS transistors.
Define the performance metric for throughput and time in embedded system.
[C] Descriptive Questions:
Explain combinational logic.
Differentiate the features of pMOs, CMOS and nMOS transistors.
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