04-05-2013, 12:47 PM
Fundamentals of Digital Electronics
[attachment=53426]
Introduction
Digital electronics is one of the fundamental courses found in all electrical
engineering and most science programs. The great variety of LabVIEW
Boolean and numeric controls/indicators, together with the wealth of
programming structures and functions, make LabVIEW an excellent tool to
visualize and demonstrate many of the fundamental concepts of digital
electronics. The inherent modularity of LabVIEW is exploited in the same
way that complex digital integrated circuits are built from circuits of less
complexity, which in turn are built from fundamental gates. This manual
is designed as a teaching resource to be used in the classroom as
demonstrations, in tutorial sessions as collaborative studies, or in the
laboratory as interactive exercises.
The order of the labs follows most electronic textbooks. The first six labs
cover the fundamental circuits of gates, encoders, binary addition,
D-latches, ring counters, and JK flip-flops. Many of the VIs are suitable for
both classroom demonstration and laboratory exploration.
The second set of six labs cover advanced topics such as DACs, ADCs,
seven-segment displays, serial communication, and the CPU. These are best
done in the context of a digital electronics lab, comparing the LabVIEW
simulations with real integrated circuits. In each case, you can enhance
simulations presented in the text by using a National Instruments DAQ
board to interact with the real world through LabVIEW digital I/O, analog
out, analog in, and serial VIs.
The AND Gate
A basic AND gate consists of two inputs and an output. If the two inputs
are A and B, the output (often called Q) is “on” only if both A and B are
also “on.”
In digital electronics, the on state is often represented by a 1 and the off state
by a 0. The relationship between the input signals and the output signals is
often summarized in a truth table, which is a tabulation of all possible inputs
and the resulting outputs. For the AND gate, there are four possible
combinations of input states: A=0, B=0; A=0, B=1; A=1, B=0; and A=1, B=1.
In the following truth table, these are listed in the left and middle columns.
The AND gate output is listed in the right column.
The OR and XOR Gates
The OR gate is also a two-input, single-output gate. Unlike the AND gate,
the output is 1 when one input, or the other, or both are 1. The OR gate
output is 0 only when both inputs are 0.
Encoders and Decoders
An encoder converts an input device state into a binary representation of
ones or zeros. Consider a rotary switch with 10 positions used to input the
numbers 0 through 9. Each switch position is to be encoded by a unique
binary sequence. For example, switch position 7 might be encoded as 0111.
A decoder performs the opposite conversion, from binary codes into output
codes.
Consider the case of a single die. On each of its six sides, one of the
following patterns appears, representing the numbers 1-6.
Modulo 6 Counter
A modulo 6 counter is any counter with six unique states that repeat in
sequence. You can build a simple modulo 6 counter using a three-element
shift register with the last element output inverted and feedback into the first
element input. (Such a counter is often called a switched tail ring counter.)
Open a new LabVIEW VI. Place three LED indicators on the front panel.
These will show the output state of the shift register elements called Q1, Q2,
and Q3. On the block diagram, use a shift register with three elements, each
wired to one LED indicator. You can use a Wait function to slow down the
action for demonstration. Note that the While Loop control is left unwired.
Each time this VI is called, the next value is returned. On the front panel,
select the three outputs as connections in the icon editor and save this
program as a subVI called Rotate.vi.
[attachment=53426]
Introduction
Digital electronics is one of the fundamental courses found in all electrical
engineering and most science programs. The great variety of LabVIEW
Boolean and numeric controls/indicators, together with the wealth of
programming structures and functions, make LabVIEW an excellent tool to
visualize and demonstrate many of the fundamental concepts of digital
electronics. The inherent modularity of LabVIEW is exploited in the same
way that complex digital integrated circuits are built from circuits of less
complexity, which in turn are built from fundamental gates. This manual
is designed as a teaching resource to be used in the classroom as
demonstrations, in tutorial sessions as collaborative studies, or in the
laboratory as interactive exercises.
The order of the labs follows most electronic textbooks. The first six labs
cover the fundamental circuits of gates, encoders, binary addition,
D-latches, ring counters, and JK flip-flops. Many of the VIs are suitable for
both classroom demonstration and laboratory exploration.
The second set of six labs cover advanced topics such as DACs, ADCs,
seven-segment displays, serial communication, and the CPU. These are best
done in the context of a digital electronics lab, comparing the LabVIEW
simulations with real integrated circuits. In each case, you can enhance
simulations presented in the text by using a National Instruments DAQ
board to interact with the real world through LabVIEW digital I/O, analog
out, analog in, and serial VIs.
The AND Gate
A basic AND gate consists of two inputs and an output. If the two inputs
are A and B, the output (often called Q) is “on” only if both A and B are
also “on.”
In digital electronics, the on state is often represented by a 1 and the off state
by a 0. The relationship between the input signals and the output signals is
often summarized in a truth table, which is a tabulation of all possible inputs
and the resulting outputs. For the AND gate, there are four possible
combinations of input states: A=0, B=0; A=0, B=1; A=1, B=0; and A=1, B=1.
In the following truth table, these are listed in the left and middle columns.
The AND gate output is listed in the right column.
The OR and XOR Gates
The OR gate is also a two-input, single-output gate. Unlike the AND gate,
the output is 1 when one input, or the other, or both are 1. The OR gate
output is 0 only when both inputs are 0.
Encoders and Decoders
An encoder converts an input device state into a binary representation of
ones or zeros. Consider a rotary switch with 10 positions used to input the
numbers 0 through 9. Each switch position is to be encoded by a unique
binary sequence. For example, switch position 7 might be encoded as 0111.
A decoder performs the opposite conversion, from binary codes into output
codes.
Consider the case of a single die. On each of its six sides, one of the
following patterns appears, representing the numbers 1-6.
Modulo 6 Counter
A modulo 6 counter is any counter with six unique states that repeat in
sequence. You can build a simple modulo 6 counter using a three-element
shift register with the last element output inverted and feedback into the first
element input. (Such a counter is often called a switched tail ring counter.)
Open a new LabVIEW VI. Place three LED indicators on the front panel.
These will show the output state of the shift register elements called Q1, Q2,
and Q3. On the block diagram, use a shift register with three elements, each
wired to one LED indicator. You can use a Wait function to slow down the
action for demonstration. Note that the While Loop control is left unwired.
Each time this VI is called, the next value is returned. On the front panel,
select the three outputs as connections in the icon editor and save this
program as a subVI called Rotate.vi.