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Combinational Circuit – MSI Circuit
ENCODER
• With the aid of K-map (don’t care situation), we can get
D0 = F1 +F2
D1 = F2 +F3
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Combinational Circuit – MSI Circuit
ENCODER (Octal to Binary)
• At one time, only one input line has a value of 1
• Most of the time needs priority encoder
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Combinational Circuit – MSI Circuit
ENCODER (Octal to Binary)
• Can you get 2n to n encoder without using Karnaugh map
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Combinational Circuit – MSI Circuit
DEMULTIPLEXER
• Given input line & sets of selection line, demultiplexer
will send data directly from input to selected output line
• Example: 1 to 4 Demultiplexer
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Combinational Circuit – MSI Circuit
DEMULTIPLEXER
• Demultiplexer is similar to decoder with enable as
follows:
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Combinational Circuit – MSI Circuit
MULTIPLEXER
• multiplexer is a device which consist of
– Several input line
– Several select line
– One output line
• It transmit one from 2n input line to one output
line using n select line. It is also known as data
selector
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Combinational Circuit – MSI Circuit
MULTIPLEXER
• Truth table for 4-1 multiplexer
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Combinational Circuit – MSI Circuit
MULTIPLEXER
• Output for multiplexer is Sum of the (product of
data lines and selection lines)
• Example: Output for 4-1 multiplexer is
• 2n-to-1 line multiplexer or 2n:1 MUX is made
from n:2n decoder with 2n input line added, for
each AND gate.
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Combinational Circuit – MSI Circuit
MULTIPLEXER
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Combinational Circuit – MSI Circuit
MULTIPLEXER
• Usage:
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Combinational Circuit – MSI Circuit
LARGE MULTIPLEXER
• Large multiplexer can be built from smaller
multiplexer
• 8:1 multiplexer can be built from smaller
multiplexer like this
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Combinational Circuit – MSI Circuit
LARGE MULTIPLEXER
• Other example the building of 8:1 multiplexer
from smaller multiplexer
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Combinational Circuit – MSI Circuit
LARGE MULTIPLEXER
• 16:1 multiplexer can be
built using five 4:1
multiplexer
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Combinational Circuit – MSI Circuit
MULTIPLEXER (Function Execution)
• Boolean Function can be executed using multiplexer
• 2n:1 multiplexer can execute Boolean function with n
input variable as the following
– Expression in SOM
Example:
– Combine n variable to n selection line
– Put 1 at data line if it is a minterm for that function,
else 0
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Combinational Circuit – MSI Circuit
MULTIPLEXER (Function Execution)
• This method succeed because
• Put 1 at I1,I2, I3, and 0 at the remaining
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Combinational Circuit (Programmable Logic Device)
Read-Only-Memory (ROM)
• Semiconductor memory is a device where data can be
stored and fetched
• Logically, this memory device can be said as memory
cells table (data)
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Combinational Circuit (Programmable Logic Device)
Read-Only-Memory (ROM)
• ROM is a memory device where data can only be read
but cannot be written
• Writing is done by special programming device
(programmable ROM)
• Any Boolean function can be executed by using ROM.
The steps: Get TT, take its input as address and output as
data
• Advantage: Boolean function is executed directly
• Disadvantage: Didn't use the “don’t care” and variable
input numbers is limited (e.g. 10 input – 1K, 16 input –
64K, 20 input – 1M)
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Combinational Circuit (Programmable Logic Device)
Read-Only-Memory (ROM)
• Ready-made ROM Device Type
– ROM: Read Only Memory
Data is written to memory by “mask programming” when
manufacturing process. High cost to start and very cost effective
if produced in large quantity
– PROM: Programmable ROM
Semi-custom chip. Fuse can be burnt with “special hardware
programming unit”. High cost for small quantity and it cannot be
erased after programmed.
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Combinational Circuit (Programmable Logic Device)
Read-Only-Memory (ROM)
• Ready-made ROM Device Type
– EPROM: Erasable PROM
Similar with PROM only that data can be erased by exposing it
to ultra violet light
– EEPROM: Electrically EPROM
PROM where data to be erased can be selected by “hardware
programmer unit” other than ultra violet light. Very useful for
isolated device where it can be reprogrammed from far
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Combinational Circuit (Programmable Logic Device)
Programmable Read-Only-Memory (PROM)
• Device with hardwired AND array (i.e. decoder) and
programmable OR array
• AND array (decoder) execute 2n minterm product
combination for n input (known as n:2n decoder)
• n line input and m line output
• Input bit variable combination – address
• Input bit combination for output line – word (each word
contain m bit)
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Programmable Read-Only-Memory (PROM)
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Programmable Read-Only-Memory (PROM)
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Programmable Read-Only-Memory (PROM)
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Combinational Circuit (Programmable Logic Device)
Execute logical function with PROM
• Example (8X3 ROM) –
• First, convert each function to SOP
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Execute logical function with PROM
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Execute logical function with PROM
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