Lattice GAL20V8B-25LP: Architecture, Key Features, and Application Design Considerations
The Lattice GAL20V8B-25LP stands as a quintessential example of a high-performance, low-power programmable logic device (PLD) from the Generic Array Logic (GAL) family. As a successor to the foundational PAL devices, it offers designers a flexible and reliable solution for implementing complex combinational and sequential logic, all while maintaining a low power footprint. Its architecture is built around a programmable AND array feeding into a fixed OR array, a structure that provides the necessary logic density for a wide range of applications.
Architectural Overview
At the core of the GAL20V8B-25LP's architecture is its programmable AND array, which drives eight Output Logic Macrocell (OLMC) units. Each macrocells is incredibly versatile, configurable by the user to operate in various modes: registered (clocked) or combinatorial (unclocked) output, with programmable polarity. This flexibility allows each output pin to function as a dedicated input, a combinatorial output, or a registered output, making the device suitable for both state machine and pure logic implementations. The "20" in its name denotes the number of inputs, while the "8" refers to the maximum number of outputs. The fixed OR array is dedicated to summing the product terms from the AND plane.
Key Features and Performance
The GAL20V8B-25LP is defined by several critical specifications that make it a durable choice for industrial and commercial designs. Its -25 suffix indicates a maximum propagation delay (tPD) of 25 nanoseconds, ensuring sufficiently high-speed operation for many control and interface logic applications. A standout feature is its ultra-low power consumption, achieved through CMOS technology, which is significantly lower than its bipolar counterparts. Furthermore, it features 100% eraseability and reprogrammability via a standard programmer, thanks to its EECMOS (Electrically Erasable CMOS) process. This reusability drastically reduces development time and cost, allowing for rapid design iteration and prototyping.
Application Design Considerations
When designing with the GAL20V8B-25LP, several factors must be meticulously considered to ensure optimal performance and reliability.
1. Power-On Reset (POR): The device features a built-in Power-On Reset circuit that ensures all registers are initialized to a known state (typically low) upon application of power. Designers must verify that this behavior aligns with their system's requirements.
2. Clock and Input Management: The dedicated clock input (Pin 1) must be handled with care to avoid skew and noise. For registered configurations, input signals must adhere to setup and hold time requirements relative to this clock to prevent metastability.
3. Output Enable Control: The Output Enable (OE) product term for each macrocell provides dynamic control over the output buffers. Efficient use of the OE can help manage bus contention in systems where the GAL interfaces with a shared data bus.
4. Product Term Limitations: Each output has a limited number of product terms available. Complex logic functions must be carefully mapped to ensure they do not exceed these limits, which might require logic optimization or partitioning.
5. Programming and Security: The device includes a security fuse that, once programmed, prevents the internal logic pattern from being read back, protecting intellectual property. However, this also means the device cannot be reprogrammed once this fuse is blown.
ICGOOODFIND
In summary, the Lattice GAL20V8B-25LP remains a highly effective and energy-efficient solution for integrating glue logic, implementing state machines, and serving as an address decoder. Its blend of speed, reprogrammability, and architectural flexibility secures its place as a valuable component in the digital designer's toolkit for both modern and legacy system designs.
Keywords: Programmable Logic Device (PLD), Output Logic Macrocell (OLMC), Low-Power CMOS, Reprogrammable, Propagation Delay (tPD).
