0. Multiplexers, Decoders, and Programmable Logic Devices
PowerPoint Presentation
Multiplexers, Decoders, and
Programmable Logic Devices
UNIT 9
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1. Figure 9.1 2-to-1 Multiplexer and Switch Analog
A multiplexer(MUX, or Data selector)
Figure to-1 Multiplexer and Switch Analog
When A is 0, the switch to the upper position, then output Z=I 0
When A is 1, the switch to the lower position, then output Z=I 1

2. Figure 9.2 Multiplexers 4-to-1 MUX, 8-to-1 MUX, and 2n-to-1 MUX
Take 4-to-1 MUX, it needs 2-control input to select 4-data input.
When AB is 00, then we Z=I0. when it is 01,10,11 is corresponding to I1,I2,I3.

3. Figure 9.3 Logic Diagram for 8-to-1 MUX
The logic diagram for a 8-to-1 MUX
Figure 9.3 Logic Diagram for 8-to-1 MUX

4. Figure 9.4 Quad Multiplexer Used to Select Data
* Multiplexers are frequently used in digital system design to select the data which
is to be processed or stored .
*How a quad MUX used to select one of two 4-bit data words…
when A=0, X0, X1,X2,X3 is appear to Zo, Z1,Z2,Z3.
Otherwise, A=1; Y0, Y1,Y2,Y3 is appear to Zo, Z1,Z2,Z3.
“Bus”
Several logic signals that perform a common
function may be grouped together to form a bus.

5. Figure 9.6 Gate Circuit with Added Buffer
A simple buffer may be used to increase the driving capability of a gate output.
Two or more gates outputs or other logic device directly connected to each other.
When one gate has 0 output(low-voltage), another has 1(high-voltage), then the
resulting output don’t clearly represented. Also damage to the gate can occurs.

6. Figure 9.7 Three-State Buffer
A Three-state buffer
Figure 9.7 Three-State Buffer
When B=1, the output C is equal to A
When B=0, the output C acts like an open circuit (High-impedance, Hi-Z)

7. Figure 9.8 Four Kinds of Three-State Buffers
Inverted input

8. Figure 9.9 Data Selection Using Three-State Buffers
When select line B is 0, D= A
Then B=1, D=C Therefore, D= B’A+ BC
This is logically equivalent to using a 2-to-1 MUX.

9. Figure 9.10 Circuit with two Three-State Buffers
Three-state Buffer shows Hi-Z(open circuit), The possible output is as-below:

10. Figure 9.11 4-Bit Adder with Four Sources for One Operand
A 4-bit adder: setup by a three-state bus buffer
Figure Bit Adder with Four Sources for One Operand
In this circuit, each buffer symbol actually represent 4 three-state buffers that
have a common enable signal.
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11. Figure 9.12 Integrated Circuit with Bi-Directional Input-Output Pin
Bi-directional pins
Figure 9.12 Integrated Circuit with Bi-Directional Input-Output Pin
The same pin used as input and output, but not both at the same time.
When buffer is Enable, the pin is driven by the output….
Then the buffer is disabled, the external source can drive the input…..
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12. Figure 9.13 A 3-to-8 Line Decoder
Decoder (3-to-8 line Decoder)
Figure 9.13 A 3-to-8 Line Decoder
Base on the 3 input variables, this decoder generate all of the minterms. Exactly one
of the output line is will be 1 for each combination of inputs
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13. Figure 9.14 A 4-to-10 Line Decoder
Decoder (A 4-to-10 line decoder)
Figure 9.14 A 4-to-10 Line Decoder
This decoder has inverted outputs exactly one
of the output will be 0

14. Figure 9.15 Realization of a Multiple-Output Circuit Using a Decoder
Decoder outputs are inverted
Figure 9.15 Realization of a Multiple-Output Circuit Using a Decoder
ORing to the output,but
for the inverted decoder
, the NAND gate used to
generate the function.

15. Figure 9.16 An 8-to-3 Priority Encoder
Encoder (A encoder performs the inverse function of a decoder)
Figure 9.16 An 8-to-3 Priority Encoder
A 8x3 encoder

16. Priority Encoder (why we need this encoder ?)
When more than one input can be 1 at the same time, the output may not the right.
for example, a 8x3 encoder, when A3=1 and A4=1 at the same time, the output is
(Y2, Y1, Y0)=(1,1,1). This is not the right output code.
That is the reason why we need a Priority encoder.
If we have y1=1, y4=1, y5=1 at the same time, based on the Priority encoder,
the highest numbered input is determined. So y5=1, then output is (101)

17. Figure 9.17 An 8-Word X 4-Bit ROM
Read-only Memories(ROM)
Figure 9.17 An 8-Word X 4-Bit ROM
Each output patterns is stored in the ROM is called a word
Each input combination serves as an address which can select one of the words
stored in the memory.
We defined a ROM (2n x m ROM), means an array of 2n words and each word
is m bits long.
(word)

18. Figure 9.18 Read-Only Memory with n inputs and m Outputs
A 2n x m ROM
Figure 9.18 Read-Only Memory with n inputs and m Outputs

19. Figure 9.19 Basic ROM Structure
A ROM basically consists of a decoder and a memory array
When a pattern is applied to the decoder input, exactly one of the 2n decoder
output is 1, this decoder output line selects one of the words in the memory
array, and the bit pattern is transferred to the memory output lines.
Figure 9.19 Basic ROM Structure
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20. Figure 9.20 An 8-Word X 4-Bit ROM
The internal structure of the 8-word x4 bit ROM
Figure 9.20 An 8-Word X 4-Bit ROM
The memory array forms the 4 output functions by ORing together selected miniterns
From previous truth table,
ORing for F0

21. Figure 9.22 Hexadecimal-to-ASCII Code Converter
Example: realize a code convertor by using ROMs
Figure 9.22 Hexadecimal-to-ASCII Code Converter
Convert a 4-bit binary code to a hexadecimal, and output the 7-bits ASCII code.
A4=A5, A6=A4’
So we only need five ouputs
4 address, creating 16 words; each words shows a 7-bit pattern!

22. Figure 9.23 ROM Realization of Code Converter
ROM realization of code convertor
Figure 9.23 ROM Realization of Code Converter
An X indicates that the switching element is present and connected, and no X
Indicate that the corresponding element is absent or not connected.

23. Read-only Memories(ROM)
mask-programmable ROMs:
a. The data is permanently stored.
b. Accomplished by selectively including or omitting the switching elements.
by using mask.
c. Expensive, not economically feasible.
Programmable ROMs(PROMs)
Electrically erasable programmable ROMs(EEPROM):
a. using special chage-stroge mechanism to enable or disable the switching
elements.
b. Suitable for the developmental phase of a digital design.
c. EEPROM can be erased and reprogrammed only a limited times( )
EEPROM

24. Figure 9.24 Programmable Logic Array Structure
Programmable logic device (PLD)
Capable of being programmed to provide a variety of different logic
functions.
2. Combinational PLD
3. Lower cost design
Figure 9.24 Programmable Logic Array Structure
Programmable logic array(PLA) : functions as ROM
For a ROM, we implements a truth table; while for a PLA, we implements a
sum-of –product expression.
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25. Figure 9.25 PLA with Three Inputs, Five Product Terms and Four Outputs
PLA which realized the same function as ROM
Figure 9.25 PLA with Three Inputs, Five Product Terms and Four Outputs
For example, F0= A’B’+AC’
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26. Figure 9.26 AND-OR Array Equivalent to Figure 9.25
PLA which realized the same function as ROM
Figure 9.26 AND-OR Array Equivalent to Figure 9.25
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27. Table 9.1 PLA Table for Figure 9.25
0: complement
1: non-complement
- : not present
0: product term not present
1: product term present
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28. Figure 9.27 PLA Realization of Equations (7-23b)
Using PLA to implement the function in Ch7(figure 7-21)
Figure 9.27 PLA Realization of Equations (7-23b)
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29. Another example of sharing gates among multiple outputs to reduce cost
Another example of sharing gates among multiple outputs to reduce cost.(From K-map)
f1 = Ʃ m(2, 3, 5, 7, 8, 9, 10, 11, 13, 15)
f2 = Ʃ m(2, 3, 5, 6, 7, 10, 11, 14, 15)
f3 = Ʃ m(6, 7, 8, 9, 13, 14, 15)
Figure 7-21

30. Minimal Solution
f1 = a′bd + abd ab′c′ + b′c
f2 = c + a′bd
f3 = bc + ab′c′ abd
After reduced
10 gates
25 gate inputs
8 gates
22 gate inputs

31. Figure 9.28 PAL Segment fixed PAL(Programmable Array Logic):
One case of PLA, while the OR array is fixed, we only programming the AND array
Figure 9.28 PAL Segment
fixed

32. Figure 9.29 Implementation of a Full Adder Using PAL
Example: Programming a PAL to implement a full adder
Figure 9.29 Implementation of a Full Adder Using PAL

33. Figure 9.30 Architecture of AsXilinx
Complex Programmable Logic Devices (CPLD)
Figure 9.30 Architecture of AsXilinx
Many PLA or PAL can be included in a CPLD chip and interconnected, a CPLD
Is actually a small digital system.
XCR3064XL contain 4 function blocks(as a PLA), each have 16 macrocells.
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34. Figure 9.31 CPLD Function Block and Marcrocell
MUX1:
Select either combinational out put(G)
or the flip-flop(Q)
Bi-directional Pin
MUX2:
Select OR-gate output(F)
or it’s complement (F’)
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35. Figure 9.32 Layout of a Typical FPGA
Field-programmable gate array (FPGA)
FPGA contain an array of logic cells(also called configurable logic blocks, CLB).
The user can program the functions based on FPGA.
Figure 9.32 Layout of a Typical FPGA

36. Figure 9.33 Simplified Configurable Logic Block (CLB)
A simplified CLB
Figure 9.33 Simplified Configurable Logic Block (CLB)
This CLB shows output: X, Y, XQ, YQ
H1 can select the function generator
A 4-input
reprogrammable ROM

37. Figure 9.34 Implementation of a Lookup Table (LUT)
The function generator (lookout table, LUT)
Figure 9.34 Implementation of a Lookup Table (LUT)

38. Figure 9.35 Function Expansion Using Kanaugh Map
Decomposition of switching functions
Decompose the function into subfunctions where each subfunction requires
only 4 variable input.
Figure 9.35 Function Expansion Using Kanaugh Map
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39. The Shannon’s expansion theorem
Figure 9.36 Realization of 5- and 6-Variable Functions with Function Generators
F (a, b, c, d)= a’ f(0,b,c,d) + a f(1,b,c,d)= a’f0+af1
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40. Ch9 HW
9.14
9.31
Problem 9.32
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