Lattice GAL16V8D-25QPI: Architecture, Key Features, and Design Applications
The Lattice GAL16V8D-25QPI stands as a quintessential example of a high-performance, low-power programmable logic device (PLD) from the Generic Array Logic (GAL) family. As a 20-pin CMOS device, it has been a cornerstone in digital logic design for decades, offering a flexible and reliable solution for integrating multiple TTL components into a single chip. Its architecture, defined speed grade, and robust feature set make it suitable for a wide range of applications, from simple glue logic to complex state machines.
Architecture: A Look Inside
The architecture of the GAL16V8D is built around a programmable AND array feeding into fixed OR arrays. This structure effectively creates a sum-of-products logic engine. The core consists of eight programmable output logic macrocells (OLMCs), which provide immense flexibility for configuring each output pin as either a combinatorial or registered (clocked) output. Each macrocell includes a flip-flop, multiplexers, and configurable feedback paths, allowing the output signal to be routed back into the AND array as an input. This feedback mechanism is crucial for implementing sequential logic like counters and shift registers. The device features 10 dedicated inputs and 8 configurable I/O pins, offering a total of 16 signals to the programmable AND array.
Key Features and Specifications
The "D" in its designation signifies a CMOS technology, which is renowned for its low power consumption. The "-25" denotes a maximum propagation delay (`tPD`) of 25 nanoseconds, ensuring swift operation for many standard logic functions. The "QPI" suffix indicates a Plastic Leaded Chip Carrier (PLCC) package. Key operational features include:
Electrically Erasable (E²) CMOS Technology: Allows the device to be reprogrammed and reconfigured numerous times, significantly accelerating the design iteration and debugging process.
User-Programmable Output Polarity: Each output can be configured for either active-high or active-low operation, simplifying interface with other logic families.
Built-in Security Fuse: This feature protects the proprietary logic design from being copied or reverse-engineered, a critical aspect for intellectual property protection.
100% Testability: The logic functionality is fully testable, ensuring high production yields and design reliability.
Low Power Consumption: A hallmark of its CMOS design, making it suitable for power-sensitive applications.
Design Applications
The GAL16V8D-25QPI excels in replacing multiple small- to medium-scale integration (SSI/MSI) TTL devices. Its primary application has historically been as "glue logic," interconnecting and translating signals between larger functional blocks like microprocessors, memory ICs, and peripheral controllers. Common design implementations include:
Address Decoding: Generating chip select signals for memory-mapped peripherals in microprocessor systems.
Bus Interface Logic: Controlling data flow and direction on bi-directional buses.
State Machine Design: Implementing finite state machines (FSMs) for control sequences.
Custom Counters and Registers: Creating counters with specific counting sequences or register files with unique load/enable conditions.
Protocol Conversion: Translating between simple serial data formats or parallel-to-serial conversion.
The Lattice GAL16V8D-25QPI remains a venerable and highly effective PLD. Its efficient E²CMOS architecture, flexible macrocell configuration, and robust 25ns performance provide a perfect blend of speed, density, and power efficiency for a vast array of digital logic consolidation tasks. While newer CPLDs and FPGAs offer greater capacity, the GAL16V8D continues to be a cost-optimal and reliable workhorse for legacy system support and new designs requiring simple, integrated logic.
Keywords:
Programmable Logic Device (PLD)
GAL Architecture
Output Logic Macrocell (OLMC)
Glue Logic
E²CMOS Technology
