Lattice GAL22V10D-10LPI: Architecture, Features, and Key Applications
The Lattice GAL22V10D-10LPI 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 electrically reprogrammable alternative to one-time programmable PAL devices, revolutionizing digital design prototyping and production. This article delves into its internal architecture, defining features, and the key applications it continues to serve.
Architecture: A Look Inside
The GAL22V10D's architecture is a masterpiece of structured programmability. The "22V10" designation is descriptive: it has 22 inputs and 10 output logic macrocells (OLMCs), each of which can be configured as an input or an output. Its core consists of a programmable AND array followed by a fixed OR array. The user-defined logic functions are created by programming the connections within the AND array, which then feed into the OR gates to form sum-of-products expressions.
The true genius of the design lies in its Output Logic Macrocell (OLMC). Each OLMC is incredibly versatile and can be individually configured through a programmable architecture control word. This allows each output to be set for various operational modes:
Combinational Logic: Output can be either active-high or active-low.
Registered Logic: Outputs can be clocked through a D-type flip-flop, enabling the implementation of sequential circuits like counters and state machines.
Complex Mode: Allows for feedback paths, where the output can be fed back into the AND array as an input.
This flexibility allowed a single GAL22V10D to replace a wide range of standard SSI and MSI logic ICs.
Key Features and Specifications
The "D" in its name signifies a robust commercial-grade temperature range (0°C to +75°C), while the "-10LPI" suffix indicates a maximum propagation delay (tPD) of 10 nanoseconds and a low-power incarnation. Its features made it a superior choice for many designs:
High-Speed Operation: The 10ns speed grade was suitable for a vast array of applications, from interface logic to complex state machines.
Electrically Erasable (EE) CMOS Technology: Unlike PALs, the GAL22V10D is reprogrammable and UV-erase is not required. This allowed for rapid design iteration, testing, and field updates.
Low Power Consumption: The advanced CMOS technology resulted in significantly lower power consumption than bipolar PAL equivalents.
100% Testability: The logic functions were fully testable, ensuring high reliability.
Security Fuse: A programmable security bit prevents unauthorized copying of the programmed configuration, protecting intellectual property.
Key Applications
While newer CPLDs and FPGAs have taken over highly complex designs, the GAL22V10D-10LPI remains relevant in numerous areas:
Address Decoding: It is perfectly suited for generating chip select and memory-mapped I/O signals in microprocessor and microcontroller-based systems.
State Machine Design: Its registered outputs make it an ideal platform for implementing medium-complexity finite state machines (FSMs).
Glue Logic Integration: Its primary historical role was to replace numerous discrete TTL logic chips (gates, flip-flops, decoders) on a PCB, reducing board space, part count, and cost.
Bus Interface and Control Logic: It is commonly used for implementing custom timing, control signals, and protocol logic for interfacing between different parts of a system.
Educational Tool: It serves as an excellent device for teaching digital logic design, from basic combinational circuits to advanced sequential systems.
The Lattice GAL22V10D-10LPI is more than just a chip; it is a foundational pillar of modern programmable logic. Its elegant blend of a programmable AND array, fixed OR array, and supremely configurable output macrocells created a universal logic device that empowered a generation of engineers. It demonstrated the clear advantages of in-system reprogrammability and integration, paving the way for the complex programmable logic devices we use today. For tasks requiring integration of logic, state machine control, and bus interfacing, it remains a capable, cost-effective, and reliable solution.
Keywords:
1. Programmable Logic Device (PLD)
2. Output Logic Macrocell (OLMC)
3. Sum-of-Products
4. Glue Logic
5. Reprogrammable
