Synchronous vs Asynchronous Counter

Synchronous Counter vs Asynchronous Counter

• Synchronous counter can operate on higher frequency than asynchronous counter as it doesn't have cumulative delay because of the same clock given to each flip-flop.
• Also known as parallel counter.

Instruction Cycle

• A program in a computer's memory unit consists of a sequence of instructions.
• The processor executes these instructions by going through a cycle for each instruction.
• The instruction cycle consists of the following phases:
  • Fetch instruction from memory.
  • Decode the instruction.
  • Read the effective address from memory.
  • Execute the instruction.

Input-Output Configuration

• Input-output devices act as an interface between the machine and the user.
• Instructions and data stored in memory come from some input device.
• Results are displayed to the user through some output device.

Instruction Format

• Instruction includes a set of operation codes and operands that manage with the operation codes.
• Instruction format supports the design of bits in an instruction.
• Contains fields including opcode, operands, and addressing mode.
• Instruction length is generally preserved in multiples of the character length, which is 8 bits.

Registers

• Registers are a type of computer memory used to quickly accept, store, and transfer data and instructions.
• Registers used by the CPU are often termed as Processor registers.
• A processor register may hold an instruction, a storage address, or any data.
• Different registers used in computer:
  • OUTR (8-bit): Output register that holds output character.
  • INPR (8-bit): Input register that holds input character.
  • PC (12-bit): Program Counter that holds the address of the instruction.
  • AR (12-bit): Address Register that holds an address for memory.
  • DR (16-bit): Data Register that holds memory operand.
  • AC (16-bit): Accumulator that holds the result of an operation.

Counter

• A counter is a device that stores (and sometimes displays) the number of times a particular event or process has occurred.
• Counters are used in digital electronics for counting purposes.
• Counters can count specific events happening in the circuit.
• They can also be designed to follow a certain sequence based on design.
• Counters are sequential circuits that count the number of pulses, can be either in binary code or BCD form.
• Main properties of a counter are timing, sequencing, and counting.
• Counters can be used as frequency dividers where the frequency of a given pulse waveform is divided.
• Counters work in two modes: Up counter and Down counter.

Types of Counters

• Asynchronous Counter: doesn't use a universal clock, only the first flip-flop is driven by the main clock, and the clock input of the rest of the following flip-flops is driven by the output of previous flip-flops.
• Synchronous Counter: has one global clock that drives each flip-flop, so output changes in parallel.

Flip Flops

• J-K Flip Flop: has Clock (CLK), Clear (CLR), and Preset (PR) inputs.
• D Flip Flop: used in synchronous counters.
• T Flip Flop: used in counters.