Lattice GAL22V10B-25LJ: Architecture, Key Features, and Target Applications
The Lattice GAL22V10B-25LJ stands as a classic 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 pin-compatible replacement for a wide array of simple PAL devices, revolutionizing digital design in its era. This article delves into the architecture, defining characteristics, and primary use cases of this iconic component.
Architecture: A Look Inside
The architecture of the GAL22V10B is elegantly structured around a programmable AND array feeding into a fixed OR array. This configuration is the hallmark of a Simple Programmable Logic Device (SPLD). The "22V10" designation is descriptive: the 22 refers to the number of inputs to the AND array, and the 10 refers to the number of output logic macrocells (OLMCs).
Each of the ten output macrocells is a sophisticated circuit that provides tremendous flexibility. Crucially, each macrocell can be individually configured by the designer to be either a combinatorial output or a registered (clocked) output. This is managed through a set of programmable product terms that control the output's behavior, including polarity (active-high or active-low). This architectural feature allowed a single GAL22V10B to emulate dozens of different fixed-function PALs, consolidating inventory and simplifying board design.
Key Features and Specifications
The GAL22V10B-25LJ's part number reveals its critical performance specs. The suffix -25 denotes a maximum propagation delay (tPD) of 25 nanoseconds, making it a capable performer for a vast range of clock speeds in its time. The LJ suffix indicates the package type, a 28-pin PLCC (Plastic Leaded Chip Carrier).
Its most significant feature was electrically erasable (E2) CMOS technology. Unlike one-time programmable (OTP) bipolar PALs, the GAL22V10B could be erased with ultraviolet light or, in later versions, electrically, allowing for countless design iterations and circuit changes. This reusability drastically accelerated prototyping and development cycles. Furthermore, it offered 100% programming yield and high reliability due to its CMOS construction, which also featured lower power consumption than its bipolar counterparts.
Target Applications
The versatility of the GAL22V10B made it a ubiquitous "glue logic" component throughout the 1990s and early 2000s. Its primary role was to replace multiple simple TTL (Transistor-Transistor Logic) chips and smaller PALs, integrating their functions into a single, reprogrammable device. Key target applications included:
Address Decoding: Generating chip select (CS) signals for microprocessors and microcontrollers in memory-mapped systems.
State Machine Control: Implementing simple finite state machines (FSMs) for controlling digital sequences.
Bus Interface Logic: Managing data flow and signal timing between different subsystems or peripherals.
I/O Port Expansion and Control: Adding and controlling additional input/output lines for embedded systems.
Signal Gating and Conditioning: Performing basic logic operations like multiplexing, demultiplexing, and waveform generation.
While modern Complex Programmable Logic Devices (CPLDs) and FPGAs have largely superseded SPLDs for new designs, the GAL22V10B remains a legendary part for educational purposes, maintaining legacy systems, and for designers who need a simple, low-cost, and proven logic integration solution.
The Lattice GAL22V10B-25LJ was a cornerstone of digital design, prized for its flexible output macrocells, reprogrammable E2CMOS technology, and role as a universal glue logic consolidator. It successfully bridged the gap between fixed TTL logic and the more complex programmable devices that followed.
Keywords:
1. Programmable Logic Device (PLD)
2. Output Logic Macrocell (OLMC)
3. Glue Logic
4. E2CMOS Technology
5. Address Decoding
