Arithmetic Logic Unit: The ALU performs arithmetic calculations and logical operations
in the binary number system.
• Shift Registers: The shift registers are temporary stores; one of them, called the accumulator
contains the data actually being processed.
• Control Unit: The control unit contains the computer’s clock. This is a crystal controlled
oscillator which generates timing pulses at a fixed frequency, typically between 120 and
45 MHz. This synchronizes computer operations.

The CPU accepts digital signals from the input devices: keyboard, mouse or modem

in the case
of a PC, via its input port. In an aircraft these could be various sensors: Rad Alt, Baro Alt, TAS,
fuel flow, etc.

• Binary System Definition:
  • The binary system is a number system with only two states or digits: 0 and 1.
  • It is the foundation of digital systems, including computers and digital electronics.
• Binary Digit (Bit):
  • A single binary digit is called a “bit.”
  • Bits are the smallest unit of data in digital systems.
• Voltage Representation in Digital Circuits:
  • In digital circuits, two different voltage levels are used to represent the binary digits 0 and 1.
  • For example, a low voltage may represent 0, and a high voltage may represent 1.
• Types of Logic:
  • Positive Logic:
    • High voltage represents 1, and low voltage represents 0.
  • Negative Logic:
    • High voltage represents 0, and low voltage represents 1.
• Codes in Digital Systems:
  • Codes are combinations of the binary states (0 and 1) used in digital systems to represent:
    • Numbers, symbols, alphabetic characters, and other types of information.
  • Examples of codes include ASCII (for text) and binary-coded decimal (BCD) for numerical data

The CPU accepts digital signals from the input devices: keyboard, mouse or modem, in the case
of a PC, via its input port. In an aircraft these could be various sensors: Rad Alt, Baro Alt, TAS,
fuel flow, etc.

After processing these are fed out via its output port to a Visual Display Unit (Monitor) or printer. In an aircraft the output may be fed to an EFIS Symbol Generator or the FMS Control
and Display Unit (CDU).

Memory that loses data in the event of a power failure or switch off is called VOLATILE
MEMORY

Memory that retains data when the power is switched off is called NON-VOLATILE MEMORY.

Memory that loses data in the event of a power failure or switch off is called VOLATILE
MEMORY

Memory that retains data when the power is switched off is called NON-VOLATILE MEMORY.

The CPU accepts digital signals from the input devices: keyboard, mouse or modem(any thing which is giving input to the system)

in the case
of a PC, via its input port. In an aircraft these could be various sensors: Rad Alt, Baro Alt, TAS,
fuel flow, etc.

A low-level programming language for computers, and other programmable devices. It is a
symbolic representation of the machine codes, and other constants, needed to program a
given CPU.
The code is usually defined by the hardware manufacturer.

Digital Computer Components (Hardware)
Having discussed the language in which computers work, and remembering that binary is the
basic language in which calculations are carried out and information is stored in memory, we
shall now look at the construction of a basic computer.
All computers have the basic components shown in the diagram below:

The smallest unit of information in a digital system is a bit, which is short for binary digit. A bit can have one of two values, usually 0 or 1

The smallest unit of information in a digital system is a bit, which is short for binary digit. A bit can have one of two values, usually 0 or 1

To convert the decimal number 7 to its binary equivalent:

1. Divide the decimal number by 2 and record the remainder.
2. Repeat the process with the quotient until the quotient becomes 0.
3. The binary equivalent is obtained by reading the remainders from bottom to top.

Steps:

• 7 ÷ 2 = 3 remainder 1
• 3 ÷ 2 = 1 remainder 1
• 1 ÷ 2 = 0 remainder 1

Binary Equivalent of 7: 111

The computer language in which calculations are carried out and information is stored in memory is binary language.

• Binary language consists of only two digits, 0 and 1.
• All computations and data storage in computers rely on this system, as it corresponds to the two states of electronic switches: on (1) and off (0).
• Higher-level programming languages (e.g., Python, Java) are eventually converted into binary instructions for the computer’s hardware to execute.

The computer language system that uses base 16 is known as Hexadecimal.

• Hexadecimal System:
  • It is a positional numeral system with a base of 16.
  • It uses the digits 0 to 9 and the letters A to F (where A = 10, B = 11, …, F = 15) to represent values.
• Usage:
  • Commonly used in computing as a more human-readable representation of binary values.
  • One hexadecimal digit corresponds to 4 binary bits, making it easier to convert between binary and hexadecimal.
• Example:
  • The binary number 1111 0000 is equivalent to the hexadecimal number F0

The computer language system that uses base 8 is called the Octal System.

• Octal System:
  • It is a positional numeral system with a base of 8.
  • It uses the digits 0 to 7 to represent values.
• Usage:
  • Octal is often used in computer systems as a shorthand for binary because one octal digit corresponds to 3 binary bits.
  • It was more commonly used in early computing for simplifying binary data representation, especially in assembly language programming.
• Example:
  • The binary number 110101 is equivalent to the octal number 65.

This is an example of Positive Logic in digital systems.

Explanation:

• Positive Logic:
  • In positive logic, high voltage (e.g., +5 volts) represents binary 1, and low voltage (or ground/earth, 0 volts) represents binary 0.
• Characteristics:
  • It is the most commonly used logic system in digital electronics.
  • It provides a straightforward way to interpret binary signals in circuits.
• Contrast with Negative Logic:
  • In negative logic, the roles are reversed: high voltage represents binary 0, and low voltage represents binary 1.

In a negative logic system, the representation of binary values is reversed compared to positive logic:

Key Points:

1. High Voltage = Binary 0
   • A higher voltage level (e.g., +5V) represents binary 0.
2. Low Voltage = Binary 1
   • A lower voltage level (e.g., 0V or ground) represents binary 1.

Usage of Negative Logic:

• Negative logic is less common but is used in specific applications where it may simplify circuit design or better suit a system’s requirements.
• It is often used in systems that involve active-low signals, such as control lines or interrupt signals (e.g., an active-low reset pin).

Example:

• A digital signal operating at 0V (low) is interpreted as 1.
• A digital signal at +5V (high) is interpreted as 0.

CPU  consists of:
• Arithmetic Logic Unit: The ALU performs arithmetic calculations and logical operations
in the binary number system.
• Shift Registers: The shift registers are temporary stores; one of them, called the accumulator
contains the data actually being processed.
• Control Unit: The control unit contains the computer’s clock. This is a crystal controlled
oscillator which generates timing pulses at a fixed frequency, typically between 120 and
45 MHz. This synchronizes computer operations

CPU itself consists of:
• Arithmetic Logic Unit: The ALU performs arithmetic calculations and logical operations
in the binary number system.
• Shift Registers: The shift registers are temporary stores; one of them, called the accumulator contains the data actually being processed.
• Control Unit: The control unit contains the computer’s clock. This is a crystal controlled
oscillator which generates timing pulses at a fixed frequency, typically between 120 and
45 MHz. This synchronizes computer operations

Analogue to Digital Conversion (A to D)
Many aircraft sensors produce analogue information in the form of varying voltages, pressures,
temperatures, etc. Of course digital computers use digital (binary) information and a device
called an Analogue to Digital Converter is required in the interface between the sensor and
the computer input device.