Lattice GAL22V10D-25LJI: Architecture, Key Features, and Target Applications
The Lattice GAL22V10D-25LJI 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 successor to simpler Programmable Array Logic (PAL) devices. Its architecture and reliability have cemented its place in numerous electronic systems, particularly those requiring complex state machine control and glue logic integration.
Architecture: A Look Inside
The architecture of the GAL22V10D is a masterpiece of programmable logic design for its era. Its name reveals its core structure: 22 inputs and 10 outputs. The internal logic is based on a programmable AND array feeding into a fixed OR array. This structure allows designers to create a wide variety of combinatorial and sequential logic functions.
The true genius of its architecture lies in its Output Logic Macrocell (OLMC). Each of the ten output pins is driven by a configurable OLMC. These macrocells provide immense flexibility, allowing each pin to be programmed independently as:
A dedicated input
A dedicated combinatorial output
A registered (clocked) output
A combinatorial I/O
A registered I/O
This programmability is managed by a set of architecture control bits, making the single GAL22V10D device a replacement for dozens of fixed-function TTL logic chips.
Key Features and Specifications
The part number "GAL22V10D-25LJI" itself encodes several of its critical features:
GAL22V10D: Denotes the core logic function (22V10) with D-type registered outputs.
-25: Signifies a maximum propagation delay of 25 nanoseconds, ensuring high-speed operation for its time.
LJ: Indicates the package type, a 28-pin PLCC (Plastic Leaded Chip Carrier).
I: Specifies the industrial operating temperature range (-40°C to +85°C).
Other paramount features include:
Electrically Erasable (EE) CMOS Technology: Unlike one-time programmable (OTP) PALs, the GAL22V10D can be erased and reprogrammed thousands of times, drastically accelerating design prototyping and debugging.
Low Power Consumption: Utilizing CMOS technology, it draws significantly less current than its bipolar PAL predecessors.
100% Testability: Advanced circuitry allows full functional testing of the programmed device, ensuring high manufacturing quality.
Security Fuse: A programmable security bit prevents the copying or reverse-engineering of the programmed logic pattern, protecting intellectual property.
Target Applications
The flexibility and integration capability of the GAL22V10D-25LJI made it a ubiquitous component in digital systems from the late 1980s through the 2000s. Its primary application domains were:
Address Decoding and Glue Logic: It was extensively used in microprocessor and microcontroller-based systems to replace discrete TTL logic chips for functions like memory address decoding, I/O port selection, and signal gating.
State Machine Design: Its registered outputs were ideal for implementing complex finite state machines (FSMs) that controlled system operation, data flow, and timing sequences.
Bus Interface and Control: The device was perfect for managing interface protocols and timing between different subsystems with varying bus standards.
Data Routing and Multiplexing: It could be programmed to handle data routing, parallel-to-serial conversion, and multiplexing tasks efficiently.
While largely supplanted by larger CPLDs and FPGAs in new designs, the GAL22V10D remains in production for supporting the maintenance and longevity of existing legacy industrial, military, and communications equipment.
The Lattice GAL22V10D-25LJI is a foundational pillar of programmable logic. Its innovative macrocell architecture, reprogrammability, and high integration density provided a critical bridge from discrete logic to advanced CPLDs, demonstrating a perfect balance of flexibility, performance, and cost-effectiveness for a generation of digital designs.
Keywords:
1. Programmable Logic Device (PLD)
2. Output Logic Macrocell (OLMC)
3. Electrically Erasable (EE)
4. Glue Logic
5. State Machine
