Lattice GAL22V10D-10LJI: Architecture, Features, and Key Applications
The Lattice GAL22V10D-10LJI 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 CMOS-based alternative to the older, one-time programmable PAL devices. Its architecture became a industry standard for implementing a wide range of digital logic functions in an efficient and cost-effective manner.
Architecture and Core Features
The architecture of the GAL22V10D is elegantly simple yet profoundly flexible. The "22V10" designation is key to understanding its structure: it features 22 inputs and 10 output logic macrocells (OLMCs). Each macrocell can be configured independently, providing tremendous design versatility.
The core of the device is a programmable AND array that feeds a fixed OR array. The AND array generates product terms from the input signals. A critical innovation of the GAL family, and a key feature of the 22V10, is the output logic macrocell (OLMC). Each OLMC can be configured by the designer to be combinational or registered (sequential), and to be an active-high or active-low output. This programmability allows a single GAL device to replace numerous fixed-function TTL logic chips, drastically reducing board space and component count.
Specific features of the Lattice GAL22V10D-10LJI include:
High-Speed Performance: The "-10" suffix denotes a maximum pin-to-pin propagation delay of 10 ns, making it suitable for high-performance state machines and critical control paths.
Low Power Consumption: Built on CMOS technology, it offers significantly lower power consumption than its bipolar predecessors.
Electrically Erasable (EE) CMOS: The device is reprogrammable and erasable, allowing for rapid design iteration and bug fixes without discarding hardware. This was a major advantage over OTP (One-Time Programmable) parts.
10 Output Logic Macrocells: Each with a programmable architecture register and polarity.
100% Testability: The logic functions are fully testable, ensuring high reliability.
Key Applications
The flexibility of the GAL22V10D made it a ubiquitous component in digital systems from the late 1980s through the 2000s. Its primary role was to act as a "glue logic" component, integrating and interfacing between larger-scale integrated circuits like microprocessors, memory, and ASICs.
Its key applications included:
Address Decoding: Generating chip select signals for memory maps in microprocessor-based systems.
State Machine Design: Implementing finite state machines (FSMs) for control units.
Bus Interface Logic: Managing data flow and control signals between different bus architectures.
I/O Port Expansion and Control: Controlling peripheral devices and decoding I/O addresses.
Converting TTL Logic: Replacing large boards full of simple 74-series logic gates with a single, programmable chip.
While largely superseded by more complex CPLDs and FPGAs for new designs, the GAL22V10D remains in use for legacy system maintenance, repairs, and in applications where its simplicity and cost-effectiveness are perfectly adequate.
The Lattice GAL22V10D-10LJI is a cornerstone of programmable logic history. Its innovative macrocell architecture, reprogrammability, and high speed established a new benchmark for logic integration. It empowered designers to consolidate complex digital circuits, dramatically accelerating prototyping and reducing time-to-market for countless electronic products. Its legacy is evident in every modern CPLD and FPGA that continues to use and expand upon the fundamental concepts it popularized.
Keywords: Programmable Logic Device, Output Logic Macrocell, Glue Logic, CMOS Technology, Address Decoding
