Parity Generators and Checkers
A parity generator/checker is a low-cost single-bit error detection solution suitable for digital systems with high real-time requirements. When designing, it is necessary to focus on logic level compatibility, timing, and anti-interference ability, and verify parameter reliability through professional instruments.
1. What is the Function and Principle of Parity Generators and Checkers?
1) Core Function: Used to detect single-bit errors 1 caused by noise or faults in digital systems (such as data transmission and storage processes). Its mechanism is to add an additional bit (parity bit) to keep the total number of binary “1”s in the transmitted data to an even number (even parity) or an odd number (odd parity).
2) Working Principle:
Generator: Calculate the number of “1”s in the input data bits and output the corresponding parity bit (if it is even parity, “1” is output when it is an even number).
Checker: Receive data bits and parity bits, calculate the number of “1”s in the data bits, and combine the received parity bits to determine whether the overall parity meets expectations (even/odd), and output the check result (such as ΣEVEN or ΣODD status).
Logic Implementation: The basic circuit is usually composed of an exclusive OR gate (XOR) because its characteristics are suitable for parity calculation.
2. Typical Devices and Implementation of Parity Generators and Checkers
1) IC Examples:
74HC280 / SN74AS280, etc.: Standard 9-bit parity generator/checker chip. Provides two output pins: ΣEVEN (even parity output) and ΣODD (odd parity output). When the number of “1” in the input data is even, ΣEVEN outputs a high level; when it is odd, ΣODD outputs a high level.
Expandability: Multiple devices can be cascaded (such as connecting the ΣEVEN output of the previous stage to the data input of the next stage) to support more than 9 bits (such as 16 bits) of data verification.
2) Design Technology Evolution:
Hardware Description Language (HDL): Such as AHDL/VHDL, can be used to describe and implement parity check circuit logic.
Emerging Technologies:
Quantum dot cellular automata (QCA): Nanoscale devices, designed parity generators/checkers based on QCA-XOR/XNOR gates, with low power consumption and high-density potential.
Optical implementation: Using Savart plates and spatial light modulators (SLMs) to build optical path parity checkers in modified ternary systems (MTNs) to meet high-speed communication needs.
3. What are Parity Generators and Checkers Used for?
Data Transmission Systems: In chip-to-chip, board-to-board, or system-to-system communication links, appending parity bits and checking them at the receiving end is an economical and effective way to detect single-bit flip errors during transmission.
Memory Check: Used to detect bit errors when reading/writing memory.
High-Reliability Systems: As a basic error detection mechanism, it is used in situations where preliminary error screening is required. Because it can only detect an odd number of error bits, it is often used in combination with other more powerful error correction codes (ECC).