Lattice GAL22V10D-25LPI: Architecture, Key Features, and Target Applications
The Lattice GAL22V10D-25LPI 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 a wide array of simple PAL devices, revolutionizing digital design in its era. Its architecture, performance, and reliability made it a cornerstone for countless electronic systems.
Architecture
The GAL22V10D is built around a programmable AND array feeding into a fixed OR array. This structure allows designers to create custom sum-of-products logic functions. The "22V10" designation is key: it has 22 inputs and 10 output logic macro cells (OLMCs). Each macrocell is highly versatile, configurable for combinatorial or registered (clocked) output operations. A critical architectural advantage was its use of Electrically Erasable (E2) CMOS technology, which allowed the device to be reprogrammed multiple times, a significant improvement over one-time programmable (OTP) bipolar PALs. The onboard logic allocator and programmable output polarity further enhanced its flexibility.
Key Features
The specific "-25LPI" suffix denotes two critical characteristics: its speed grade and package type. It features a maximum propagation delay (tPD) of 25ns, which was a strong performance metric for its time, enabling its use in moderately high-speed applications. "LPI" indicates the package is a 28-pin Leaded Plastic Injection package, a standard through-hole DIP format ideal for prototyping and production.
Its most celebrated feature was its 100% pin-out and function compatibility with a broad range of 24-pin PAL devices like the PAL16L8 and PAL16R8. This made it a drop-in replacement that offered re-programmability. Furthermore, it incorporated advanced features like a programmable register preload for predictable testability and integrated security bit to prevent unauthorized copying of the programmed logic pattern.
Target Applications
The reprogrammability and density of the GAL22V10D-25LPI made it exceptionally popular across a vast spectrum of digital circuits. Its primary role was in glue logic integration, where it was used to replace multiple discrete TTL chips for address decoding, bus interfacing, and state machine control in microprocessor-based systems. It found extensive use in:
Computer Peripherals: Hard drive controllers, graphics cards, and printer control.
Telecommunications Equipment: For interface and control logic in routers, switches, and modems.
Industrial Control Systems: Implementing custom state machines and sequencers for automation.
Military and Aerospace: Its predictable timing and reliability were valued in these critical sectors.
Prototyping and Education: Its ease of use and re-programmability made it an ideal tool for teaching digital logic design and for verifying circuit designs before committing to an ASIC.
The Lattice GAL22V10D-25LPI is more than just a historic component; it is a testament to a pivotal shift in digital design methodology. It empowered a generation of engineers by offering a flexible, reliable, and cost-effective solution for integrating logic, dramatically reducing system complexity and time-to-market. Its legacy lies in paving the way for the more complex CPLDs and FPGAs that followed.
Keywords:
Programmable Logic Device (PLD)
Generic Array Logic (GAL)
Output Logic Macro Cell (OLMC)
Electrically Erasable CMOS (E2CMOS)
Glue Logic
