Lattice GAL22V10B-15LP: Architecture, Features, and Key Applications in Digital Logic Design
The Lattice GAL22V10B-15LP stands as a quintessential and highly influential device in the history of programmable logic. As a member of the Generic Array Logic (GAL) family, it provided a powerful, erasable, and CMOS-based alternative to the then-prevalent PAL devices, offering designers unparalleled flexibility and efficiency in digital logic design.
Architecture: A Look Inside
The architecture of the GAL22V10B-15LP is a sophisticated yet elegantly structured array of programmable logic elements. Its name reveals its core configuration: 22 inputs and 10 output logic macrocells (OLMCs). The internal structure is built around a programmable AND array that feeds into a fixed OR array. This foundational "AND-OR" structure is ideal for implementing sum-of-products (SOP) logic functions, the bedrock of combinatorial logic.
The true genius of its architecture lies in the configurability of its 10 output macrocells. Each macrocell can be individually programmed to operate as a dedicated combinatorial output, a registered (clocked) output, or even as an input. This is controlled by a set of programmable product terms that manage the output's polarity, clock source, and feedback path. This macrocell flexibility allows a single device to replace numerous standard fixed-function logic ICs, dramatically reducing board space and component count.
Key Features and Advantages
The GAL22V10B-15LP-15LP is defined by a set of features that made it a workhorse for a generation of engineers:
High-Speed Performance: The -15LP suffix denotes a maximum propagation delay of 15 nanoseconds, making it suitable for high-speed state machines and complex combinatorial logic.
Low Power Consumption: Fabricated in advanced CMOS technology, it offers significantly lower power consumption than its bipolar (TTL) predecessors, a critical advantage for power-sensitive applications.
Electrically Erasable (E²CMOS) Technology: Unlike one-time programmable (OTP) PALs, the GAL22V10B is reprogrammable. This allows for rapid design iteration, prototyping, and field upgrades, drastically reducing development time and cost.
100% Testability & High Reliability: The architecture supports functional testing, ensuring that programmed devices can be thoroughly verified. Its CMOS construction also contributes to high noise immunity and overall circuit reliability.
Registered or Combinatorial Outputs: The programmable macrocells provide the ultimate choice for implementing either sequential logic (with registers) or pure combinatorial logic.
Key Applications in Digital Logic Design
The versatility of the GAL22V10B-15LP allowed it to be deployed in a vast array of digital systems throughout the 1990s and early 2000s. Its primary applications included:
Address Decoding: It was exceptionally well-suited for generating chip-select signals in microprocessor and microcontroller-based systems, replacing multiple 74-series decoders like the 74HC138.
State Machine Design: The device's registered outputs and fast clock-to-output times made it ideal for implementing medium-complexity finite state machines (FSMs) for control logic.
Bus Interface and Control Logic: It was commonly used to glue together complex ICs with different interface timings, acting as a customized "glue logic" controller for managing data flow, read/write signals, and bus arbitration.
Code Converters and Shift Registers: Designers could easily program the device to function as parallel-to-serial converters, sequence detectors, or custom arithmetic logic units (ALUs).
The Lattice GAL22V10B-15LP was more than just a chip; it was a cornerstone of digital prototyping and production. It empowered a generation of engineers to consolidate complex logic into a single, reprogrammable device, bridging the gap between discrete logic and high-density FPGAs/CPLDs. Its legacy lies in democratizing programmable logic, making it accessible, affordable, and essential for countless electronic designs.
Keywords
Programmable Logic Device (PLD)
Generic Array Logic (GAL)
Output Logic Macrocell (OLMC)
Sum-of-Products (SOP)
Glue Logic
