Digital Technology –
Many electronic devices are computer controlled .a cell phone, TV, or even your car has digital circuits at work. Understanding these devices is critical to anyone working in electronics today.
The electrical world is comprised of two types of circuits; the first is the linear electrical circuit in a linear world voltages can vary from microvolts to 10’s of thousand of volts. We experience this world from a speaker pushing out sound or a TV display. the control for these devices generally uses the digital world .Digital devices live in two states, on is on – a voltage of 5v or off – a voltage of 0 volts. A circuit being only on or off has many restrictions in doing electrical work demanded by electrical products.
The advantage of digital circuits is found in the interface with linear devices and interfaces to analog output circuits. For example, in a car you may speak to the car take your linear world to raise the volume on the radio.
Digital signal processing
In digital circuits, many wires are needed to send on -off signals of 0 and 5 volts to circuit devices. If a digital IC chip or transistor sees 0 volts it assigns number 0 to the input or 0 output. If it experiences a 5 volts signal, it would assign a 1 to the input or output of the devices. We can see this with a logic probe or voltmeter by a voltage measurement.
If we only used one wire, the amount of decoded information would be limited to two states – a 0 or 1. Digital devices must have more inputs to do useful work; they use groups of wires called a bus. This could be 8 wires, 16, 32 or even 64 inputs or outputs
If we look at just four inputs there will be 16 combinations of on-off signals. The lowest inputs would be 0000 and the highest would be 1111.
See the following table to see how this works, you decoded 16 differing
| Input or output – 0 or 1 | Number | Computer number |
| 0000 | 0 | 0 |
| 0001 | 1 | 1 |
| 0010 | 2 | 3 |
| 0011 | 3 | 4 |
| 0100 | 4 | 4 |
| 0101 | 5 | 5 |
| 0110 | 6 | 6 |
| 0111 | 7 | 7 |
| 1000 | 8 | 8 |
| 1001 | 9 | 9 |
| 1010 | 10 | A |
| 1011 | 11 | B |
| 1010 | 12 | C |
| 1011 | 13 | D |
| 1110 | 14 | E |
| 1111 | 15 | F |
BASIC DIGITAL CONCEPTS
Bytes, Nibbles, and Bits
In the analysis of digital devices, the combination of input signals (changing states) is how a technician would look for faults. If a signal is missing or in providing a wrong combination of input /output, a circuit problem may exist. Generally, no output or input would be found.
To make life easy for design and troubleshooting, the wires that carry on off signal are grouped in combination or 4 wires called nibbles. Therefore, an eight wire address bus would have wires 1 -4 as one group and 4 -8 as another group. Each group of four will give you a nibbles with a measurement of 0 to F based on the combination of 0’s and 1’s on each wire. Group 2 wires 4 -8 would be a separate Nibbles. With 2 nibbles you have an eight wire Byte. So, two nibbles make a byte. Each wire is called a Bit. So, input four bits make a nibble; eight bits will make one byte. An example of this might be the address for an input bus. Let’s say that input jack 1 has address of F2, so if we measured each wire we could find input pin 1-4 would be 1111 and pins 4-8 would be 0010.
Computer code is measured in nibbles – 16 wire address bus would have 4 nibbles – example F5 A6. As shown, each byte is separated by a space. The number system used in computers is base is called 16 hexadecimal. The numbering system of 8 is called octal. The other term used with digital devices is activity. Because the input and output signal can change at high rates of speed. If activity is to be measured it must be sampled and then analyzed or watched in real time to indicate the chips are functioning by processing correct data. In some circuit, the level is static and easily measured.
A digital chip must rise to a voltage level of 5- volts or sink to a ground – 0 Volts. A defective chip may fail to do this, the measured results can be lower than or higher than expected voltage. Shorts or too much current draw from the output pin of a digital chip may result in lower output voltage but not be a failure within device. Too much of a current draw from downstream devices can cause a shut off of an output high signal. The result is that troubleshooting can become complex, opening circuit output are rechecking may show the condition of the device.