Digital ICs Education

NAND and NOR gates possess a special property: they are universal. That is, given enough gates, either type of gate is able to mimic the operation of any other gate type. For example, it is possible to build a circuit exhibiting the OR function using three interconnected NAND gates. The ability for a single gate type to be able to mimic any other gate type is one enjoyed only by

PARTS AND MATERIALS Two AAA Batteries Battery Clip (Radio Shack catalog # 270-398B) U1, U2 - CMOS TLC555 timer IC (Radio Shack catalog # 276-1718 or equivalent) Q1 - 2N3906 PNP Transistor (Radio Shack catalog #276-1604 (15 pack) or equivalent) Q2 - 2N2222 NPN Transistor (Radio Shack catalog #276-1617 (15 pack) or equivalent) D1 - Red light-emitting diode (Radio Shack catalog # 276-041 or equivalent) D2 - Blue light-emitting diode (Radio Shack catalog # 276-311

Hey we are in 15-3 and in this section we are going to be looking at sequential logic. This section will actually be broken into multiple sections. A sequential logic circuit can have any number of inputs and any number of outputs. Now this is much like what we discussed in combinational logic. A sequential logic circuit typically has some type of memory element to hold the state of the

The 555 integrated circuit is the most popular chip ever manufactured. Independently manufactured by more than 10 manufacturers, still in current production, and almost 40 years old, this little circuit has withstood the test of time. It has been redesigned, improved, and reconfigured in many ways, yet the original design can be bought from many vendors. The design of this chip was right the first time. Originally conceived in 1970 and created by Hans

Suppose we altered our basic open-collector inverter circuit, adding a second input terminal just like the first: This schematic illustrates a real circuit, but it isn’t called a “two-input inverter.” Through analysis, we will discover what this Circuit’s logic function is and correspondingly what it should be designated as. Just as in the case of the inverter and buffer, the “steering” diode cluster marked “Q1” is actually formed

Counting practice: count from zero to thirty-one in binary, octal, and hexadecimal:

As a first example of useful combinational logic, let’s build a device that can add two binary digits together. We can quickly calculate what the answers should be: 0 + 0 = 0 0 + 1 = 1 1 + 0 = 1 1 + 1 = 102 So we well need two inputs (a and b) and two outputs. The low order output will be called Σ because it represents the sum, and the high order output will be called Cout because it represents the carry out. The truth

Perhaps the most ingenious technique was that of the delay line. A delay line is any kind of device which delays the propagation of a pulse or wave signal. If you’ve ever heard a sound echo back and forth through a canyon or cave, you’ve experienced an audio delay line: the noise wave travels at the speed of sound, bouncing off of walls and reversing direction of travel.

A demultiplexer, sometimes abbreviated dmux, is a circuit that has one input and more than one output. It is used when a circuit wishes to send a signal to one of many devices. This description sounds similar to the description given for a decoder, but a decoder is used to select among many devices while a demultiplexer is used to send a signal among many devices. A demultiplexer is used

PARTS AND MATERIALS 4017 decade counter/divider (Radio Shack catalog # 276-2417) 555 timer IC (Radio Shack catalog # 276-1723) Ten-segment bargraph LED (Radio Shack catalog # 276-081) One SPST switch One 6 volt battery 10 kΩ resistor 1 MΩ resistor 0.1 µF capacitor (Radio Shack catalog # 272-135 or equivalent) Coupling capacitor, 0.047 to 0.001 µF Ten 470 Ω resistors Audio detector with headphones Caution! The 4017 IC is CMOS, and therefore sensitive to static electricity! Any single-pole, single-throw switch is adequate. A household

Parallel-in/ serial-out shift registers do everything that the previous serial-in/ serial-out shift registers do plus input data to all stages simultaneously. The parallel-in/ serial-out shift register stores data, shifts it on a clock by clock basis, and delays it by the number of stages times the clock period. In addition, parallel-in/ serial-out really means that we can load data in parallel into all stages before any shifting ever begins. This

A bistable multivibrator has two stable states, as indicated by the prefix bi in its name. Typically, one state is referred to as set and the other as reset. The simplest bistable device, therefore, is known as a set-reset, or S-R, latch. To create an S-R latch, we can wire two NOR gates in such a way that the output of one feeds back to the input of another, and

Identify the type of logic gate shown in this schematic diagram, and explain why it has the name it does:

Diodes can perform switching and digital logic operations. Forward and reverse bias switch a diode between the low and high impedance states, respectively. Thus, it serves as a switch. Logic Diodes can perform digital logic functions: AND, and OR. Diode logic was used in early digital computers. It only finds limited application today. Sometimes it is convenient to fashion a single logic gate from a few diodes. Diode AND gate

So far, we’ve studied both S-R and D latch circuits with enable inputs. The latch responds to the data inputs (S-R or D) only when the enable input is activated. In many digital applications, however, it is desirable to limit the responsiveness of a latch circuit to a very short period of time instead of the entire duration that the enabling input is activated. One method of enabling a

We’ve already seen one example of a monostable multivibrator in use: the pulse detector used within the circuitry of flip-flops, to enable the latch portion for a brief time when the clock input signal transitions from either low to high or high to low. The pulse detector is classified as a monostable multivibrator because it has only one stable state. By stable, I mean a state of output where

What factors determine where potentiometers Rpot1 and Rpot2 must be set? Why are they “trimmer” potentiometers (as indicated by the special wiper symbol) and not regular panel-mount potentiometers?

Inverters and buffers exhaust the possibilities for single-input gate circuits. What more can be done with a single logic signal but to buffer it or invert it? To explore more logic gate possibilities, we must add more input terminals to the circuit(s). Adding more input terminals to a logic gate increases the number of input state possibilities. With a single-input gate such as the inverter or buffer, there can

A decoder is a circuit that changes a code into a set of signals. It is called a decoder because it does the reverse of encoding, but we will begin our study of encoders and decoders with decoders because they are simpler to design. Types of Decoders Line Decoder A common type of decoder is the line decoder which takes an n-digit binary number and decodes it into 2n data

One element conspicuously missing from the set of Boolean operations is that of Exclusive-OR. Whereas the OR function is equivalent to Boolean addition, the AND function to Boolean multiplication, and the NOT function (inverter) to Boolean complementation, there is no direct Boolean equivalent for Exclusive-OR. This hasn’t stopped people from developing a symbol to represent it, though: This symbol is seldom used in Boolean expressions because the identities, laws,