Lattice GAL22V10D-15LJ: Architecture, Key Features, and Application Design Considerations
The Lattice GAL22V10D-15LJ represents a classic and highly influential device in the realm of programmable logic. As a member of the Generic Array Logic (GAL) family, it provided a powerful, erasable, and pin-compatible successor to older PAL devices, offering designers significant flexibility. This article delves into its internal architecture, outlines its key specifications, and discusses critical considerations for employing it in modern design contexts.
Architecture: A Look Inside
The architecture of the GAL22V10D is a masterpiece of structured programmability. Its name reveals its core configuration: 22 inputs and 10 output logic macrocells (OLMCs). The internal structure is based on a programmable AND array feeding into a fixed OR array, a design known as Sum-of-Products (SoP).
The heart of the device is its 10 output logic macrocells. Each macrocell is incredibly versatile and can be configured by the user to operate in various modes:
Registered Mode: The output is clocked through a D-type flip-flop, enabling synchronous state machine design and counter applications.
Combinatorial Mode: The output is a direct function of the input product terms, suitable for simple logic decoding.
Programmable Polarity: A unique feature allowing each output to be configured as either active-high or active-low. This simplifies logic design by often reducing the number of product terms required.
The -15LJ suffix specifically denotes a 15 ns maximum propagation delay (tPD) and a leadless (J-lead) PLCC package.
Key Features and Specifications
The GAL22V10D-15LJ brought several advantages that solidified its popularity:
High-Speed Performance: With a 15 ns maximum propagation delay, it was suitable for high-performance state machines and critical control paths.
Electrically Erasable (EECMOS) Technology: Unlike one-time programmable (OTP) PALs, the GAL22V10D is UV-erasable or electrically erasable, allowing for countless design iterations and reprogramming.
100% Testability: The architecture supports full functional testing, ensuring high reliability.
Low Power Consumption: The advanced EECMOS process offered a good balance of speed and power efficiency compared to bipolar alternatives.
Pin-Compatible Replacement: It was designed as a drop-in replacement for a wide range of PAL devices like the PAL22V10, allowing for easy design upgrades.
Application Design Considerations
While a venerable component, designing with the GAL22V10D-15LJ requires attention to specific details:
1. Power-On Reset (POR): The internal registers have a defined power-on state, which is crucial for ensuring finite state machines boot into a known, safe condition.
2. Clock and Input Timing: The 15 ns speed grade must be rigorously verified against system clock frequencies. Setup and hold times for registered inputs must be met to ensure reliable operation.
3. Product Term Limitations: Each output has a limited number of dedicated product terms. Complex logic functions must be carefully designed or partitioned to fit within these constraints.
4. Modern Tooling: While still supported, designing with this legacy PLD requires older or specialized software tools (like CUPL or WinCupl) for logic synthesis and JEDEC file generation.
5. Obsolescence and Alternatives: As an older technology, its primary application today is in maintaining and supporting existing legacy systems. For new designs, modern CPLDs or FPGAs from Lattice Semiconductor offer far greater density, integration, and features.
ICGOOODFIND
The Lattice GAL22V10D-15LJ was a cornerstone of digital design, offering an unparalleled blend of speed, flexibility, and reprogrammability for its era. Its well-defined architecture of a programmable AND array and configurable output macrocells empowered a generation of engineers. Understanding its features and design constraints remains valuable for maintaining legacy systems and appreciating the evolution of programmable logic.
Keywords:
Programmable Logic Device (PLD)
Output Logic Macrocell (OLMC)
Sum-of-Products (SoP)
Propagation Delay (tPD)
JEDEC File
