21-09-2012, 03:55 PM
Fundamentals of Digital Electronics
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.
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.
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.
Memory: The D-Latch
In the first three labs in this series, all your work has been with
combinational circuits in which the input states completely determine the
output states. In the circuits thus far, there is no dependence on past history
or how you arrived at the current state. This means that “remembering”
cannot be built into the circuits. Most digital operations are sequential, in
that event B must occur after event A. Furthermore, in a digital computer,
events are not only sequential but also synchronous with some external
clock. Clocked logic devices are devices whose output changes only when
a clock signal is asserted. In the next few labs, you will see how the addition
of clocked logic devices brings memory into digital circuits, making it
possible to construct many interesting digital circuits.
One simple memory circuit is called the data latch, or D-latch. This is a
device which, when “told” to do so via the clock input, notes the state of its
input and holds that state at its output. The output state remains unchanged
even if the input state changes, until another update request is received.
Traditionally, the input of the D-latch is designated by D and the latched
output by Q. The update command is provided by asserting the clock input
in the form of a transition (from HI to LO) or (from LO to HI), so-called
edge-triggered devices or level triggered devices, where the output follows
the input whenever the clock is HI.
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.
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.
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.
Memory: The D-Latch
In the first three labs in this series, all your work has been with
combinational circuits in which the input states completely determine the
output states. In the circuits thus far, there is no dependence on past history
or how you arrived at the current state. This means that “remembering”
cannot be built into the circuits. Most digital operations are sequential, in
that event B must occur after event A. Furthermore, in a digital computer,
events are not only sequential but also synchronous with some external
clock. Clocked logic devices are devices whose output changes only when
a clock signal is asserted. In the next few labs, you will see how the addition
of clocked logic devices brings memory into digital circuits, making it
possible to construct many interesting digital circuits.
One simple memory circuit is called the data latch, or D-latch. This is a
device which, when “told” to do so via the clock input, notes the state of its
input and holds that state at its output. The output state remains unchanged
even if the input state changes, until another update request is received.
Traditionally, the input of the D-latch is designated by D and the latched
output by Q. The update command is provided by asserting the clock input
in the form of a transition (from HI to LO) or (from LO to HI), so-called
edge-triggered devices or level triggered devices, where the output follows
the input whenever the clock is HI.