Digital Logic &
Computer
Architecture: A
Glimpse
In this presentation we will explore key concepts in digital logic and
computer architecture. We'll cover essential components like
latches, different number systems, and programmable logic devices.
Latches: The Building Blocks of Memory
1
SR Latch
2
D Latch
The SR latch, a fundamental
The D latch, a variation of the
building block, uses two cross-
SR latch, uses a single data
coupled NOR or NAND gates to
input (D) and a clock signal to
store a single bit of data.
store data.
SR Latch:
D Latch:
Number Systems: The
Language of Computers
Decimal
Base 10
0-9
Binary
Base 2
0-1
Octal
Base 8
0-7
Hexadecimal
Base 16
0-9, A-F
Conversions: Bridging the Gap
1
Decimal to Binary
Repeatedly divide the decimal number by 2, noting the remainders,
until the quotient is 0. The remainders, read in reverse order, form the
binary equivalent.
2
Octal to Decimal
Multiply each digit of the octal number by its corresponding power of 8
and sum the results. For example, 123(octal) = 1*8^2 + 2*8^1 + 3*8^0 = 64
+ 16 + 3 = 83 (decimal).
3
Binary to Decimal
Multiply each binary digit by its corresponding power of 2 and sum the
results. For example, 1011(binary) = 1*2^3 + 0*2^2 + 1*2^1 + 1*2^0 = 8 + 0
+ 2 + 1 = 11 (decimal).
Gray Code: A Unique Encoding System
Gray Code
Conversions
A non-weighted code where only one bit changes
To convert from binary to gray code, XOR the first bit
between successive numbers, minimizing errors in
with the second, the second with the third, and so on.
digital circuits.
For gray code to binary, convert to binary and then
repeatedly XOR adjacent bits, starting from the most
significant bit.
Programmable Logic Devices (PLDs): Versatile Logic
Solutions
PAL (Programmable Array Logic)
CPLD (Complex Programmable
Logic Device)
FPGA (Field-Programmable Gate
Array)
array. PALs offer lower density and simpler
More complex than PALs with multiple logic
Highly flexible with a large number of
implementation compared to CPLDs.
blocks interconnected by programmable
configurable logic blocks and routing
routing channels. CPLDs provide more
resources, allowing the implementation of
flexibility and higher logic density.
complex designs.
Fixed AND array and programmable OR
Programmable Read Only Memory:
• Read-Only Memory or ROM is a memory device, which collects binary information permanently.
• That implies we cannot change that saved information by any means later.
• If in case the ROM has a programmable feature, then it is named Programmable ROM (PROM).
This gives the user the flexibility to program the binary data electrically once by applying for the
PROM program.
• PROM is a programmable logic device that has a fixed AND array & a Programmable OR array.
Programmable Array Logic (PALs):
• Programmable Array Logic (PAL) is a commonly practiced programmable logic device. It
possesses a programmable AND array and a fixed OR array.
• As only the AND array is programmable, it is simpler to use but not flexible as compared to the
Programmable Logic Array.
• AND gates are programmable which implies each AND gate has both complemented and
uncomplemented inputs of variables.
• While the OR gates are not of programmable type implies the number of inputs to each OR gate
will be of fixed type.
Programmable Logic Arrays (PLAs): Building
Custom Circuits
AND Plane
OR Plane
Programmability
An array of AND gates that
An array of OR gates that combine
PLAs allow customization by setting
implement the product terms of the
the product terms to form the final
or clearing fusible links, enabling the
Boolean function.
output.
implementation of different logic
functions.
FPGA: Unlocking the Power
of Reconfigurability
Logic Blocks
The fundamental building blocks of FPGAs, capable of
implementing basic logic functions.
Routing Channels
Interconnect paths that connect the logic blocks, allowing for
flexible circuit design.
Programmable Switches
Configurable switches that control the flow of data between logic
blocks and routing channels, allowing for circuit reconfiguration.
CPLD: A Practical Choice for Logic Design
Logic Blocks
Routing Channels
Basic logic units capable of implementing logic functions.
Programmable interconnections that connect logic
blocks, enabling flexible circuit design.
CPLD Overview: A Powerful
and Versatile Tool
1
Flexibility
CPLDs offer a balance between flexibility and performance, making
them suitable for various applications.
2
Density
CPLDs provide a higher logic density compared to PALs, enabling
more complex designs.
3
Applications
CPLDs are widely used in digital systems, including control circuits,
peripheral interfaces, and communication protocols.
Thank You