Lattice GAL22V10D-25LPNI: Architecture, Key Features, and Target Applications
The Lattice GAL22V10D-25LPNI 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 earlier one-time programmable PAL devices, revolutionizing digital design prototyping and production. This article delves into its internal architecture, its defining characteristics, and the modern applications where it remains relevant.
Architecture: A Look Inside
The GAL22V10D's architecture is a masterpiece of structured programmability. Its name reveals its core configuration: 22 inputs and 10 outputs. The "D" signifies a CMOS technology variant, offering lower power consumption than its bipolar predecessors.
At its heart lies a programmable AND array followed by a fixed OR array. The 22 input terms are fed into the AND array, where product terms are created based on the user's programming. A key architectural advancement of this device is its Output Logic Macrocell (OLMC). Each of the 10 outputs is driven by its own configurable OLMC, which can be programmed to be combinatorial or registered (sequential). Crucially, the macrocells provide immense flexibility, allowing each output to be configured as an input, a combinatorial output, or a registered output with programmable polarity. This eliminates the need for multiple fixed-function parts and consolidates logic into a single, universal chip.
Key Features and Specifications
The "25LPNI" suffix provides critical performance and package information:
-25: Denotes a maximum pin-to-pin propagation delay of 25 nanoseconds, ensuring reliable operation for clock speeds up to tens of megahertz.
LP: Stands for Low Power CMOS technology, a significant advantage for power-sensitive designs.
NI: Indicates the package type, in this case, a 28-lead Plastic Leaded Chip Carrier (PLCC).
Other paramount features include:
Electrically Erasable (EE) CMOS Technology: Unlike fuses, the circuit configuration is stored in EEPROM cells. This allows the device to be reprogrammed thousands of times, drastically accelerating design iteration and debugging.
100% Testability: The architecture supports functional testing, ensuring high manufacturing yields.
Pin-compatibility: It was designed as a drop-in replacement for a wide range of PAL devices like the PAL22V10, allowing for easy design upgrades without board re-layout.
Target Applications
While surpassed in complexity by modern CPLDs and FPGAs, the GAL22V10D-25LPNI remains a valuable solution for numerous applications:
Glue Logic Integration: Its primary role is to replace multiple simple TTL or CMOS logic gates (e.g., 74-series ICs) for address decoding, bus interfacing, state machine control, and signal gating in larger systems.
Prototyping and Education: Its simplicity and reprogrammability make it an excellent tool for teaching digital logic design principles and for prototyping ideas before committing to an ASIC or more complex programmable logic.
Legacy System Maintenance and Repair: It is indispensable for supporting and repairing older electronic equipment where original PAL or simple GAL devices have failed. Engineers can reprogram a GAL22V10D to mimic the exact functionality of an obsolete part.
Industrial Control Systems: In non-speed-critical control applications, such as small state machines or simple sequencers for machinery, its reliability and low part count are significant benefits.
The Lattice GAL22V10D-25LPNI is more than just a chip; it is a foundational pillar of programmable logic history. It successfully combined the flexibility of reprogrammable EECMOS technology with a powerful and flexible macrocell architecture. While not suited for high-performance designs today, its value persists in integrating glue logic, educating new engineers, and sustaining critical legacy systems through its unparalleled role-as-a-drop-in replacement. It represents a perfect balance of simplicity, capability, and reliability.
Keywords:
Programmable Logic Device (PLD)
Output Logic Macrocell (OLMC)
Glue Logic
Electrically Erasable (EE) CMOS
Legacy System Maintenance
