Lattice GAL16V8B-15LD: Architecture, Features, and Application in Digital Logic Design
The Lattice GAL16V8B-15LD stands as a seminal device in the history of programmable logic, representing a highly versatile and cost-effective solution for a wide array of digital logic applications. As a member of the Generic Array Logic (GAL) family, it provided a powerful, erasable alternative to one-time programmable PAL devices, revolutionizing prototyping and low-to-medium volume production.
Architecture: A Look Inside
The architecture of the GAL16V8B-15LD is a masterpiece of configurable logic design. Its core consists of eight programmable Output Logic Macro Cells (OLMCs) surrounding a fixed programmable AND array. The "16" in its name denotes the number of dedicated inputs, while the "8" refers to the maximum number of available outputs. Each OLMC is incredibly flexible, capable of being configured by the user as a dedicated input, a dedicated output, or a bidirectional I/O pin. Crucially, the macrocell architecture can be configured for either combinatorial or registered (sequential) output operations, making the device suitable for both simple logic gates and more complex state machines.
The device is based on Electrically Erasable (EECMOS) technology, which allows it to be reprogrammed numerous times, a significant advantage over its predecessors.
Key Features and Specifications
The GAL16V8B-15LD boasts a set of features that made it an industry workhorse:
High Performance: The `-15` suffix indicates a maximum propagation delay of 15 nanoseconds, enabling operation at clock frequencies high enough for many contemporary systems of its era.
Re-programmability: Its EECMOS cells can be erased and reprogrammed, facilitating rapid design iteration and debugging.
Low Power Consumption: Compared to bipolar PALs, it offers significantly lower power dissipation, typically around 90mA.
100% Testability: The logic function implemented within the GAL is fully testable, ensuring high reliability.
UltraMOS® Advanced Technology: This proprietary manufacturing process contributed to its high speed and low power characteristics.
20-pin (15LD) Package: The "15LD" denotes a 20-pin Plastic Leaded Chip Carrier (PLCC) package, a common surface-mount form factor.
Application in Digital Logic Design
The primary application of the GAL16V8B-15LD was to integrate multiple standard TTL logic chips (like the 7400-series) into a single, compact device. This consolidation led to:
Reduced Board Space: Replacing several SSI/MSI chips with one GAL simplified PCB layout and miniaturized designs.
Improved Reliability: Fewer components on a board directly translated to higher mean time between failures (MTBF).
Design Security: Once programmed, the logic function could be protected from copying using a security fuse.
Rapid Prototyping: Designers could quickly implement and modify complex logic functions, from address decoders and state machines to bus interfaces and counters, without the need for custom IC fabrication.
While largely superseded by larger CPLDs and FPGAs today, the principles of using a GAL for logic integration remain foundational. It served as the perfect bridge between discrete logic and high-density programmable devices.
The Lattice GAL16V8B-15LD was an indispensable component for logic consolidation, offering a perfect blend of speed, flexibility, and re-programmability that empowered a generation of digital designers to create more efficient and reliable systems.
Keywords:
1. Programmable Logic Device (PLD)
2. Output Logic Macro Cell (OLMC)
3. Re-programmable
4. Logic Consolidation
5. Combinatorial and Sequential Logic
