Lattice GAL18V10B-10LJ: Architecture, Features, and Key Applications

The Lattice GAL18V10B-10LJ 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 the once-dominant but one-time-programmable (OTP) PAL devices. Its architecture, speed, and flexibility made it a cornerstone for countless digital logic designs in the late 1980s and 1990s.

Architecture: A Look Inside

The GAL18V10B-10LJ's architecture is elegantly simple yet powerfully configurable. The "18V10" designation breaks down as follows: 18 inputs and 10 outputs. Its core structure is based on a programmable AND array feeding into a fixed OR array. The key to its versatility lies in its Output Logic Macro Cells (OLMCs).

Each of the ten output pins is driven by a dedicated OLMC. These macro-cells can be individually configured by the user to operate in various modes, including:

Combinational Output: A simple active-high or active-low output from the OR array.

Registered Output: The output is passed through a D-type flip-flop, essential for implementing synchronous state machines and counters.

Complex Mode: Allows for feedback paths where an output pin can also serve as an input back into the AND array, enabling the creation of more complex logic functions like counters and shift registers.

This reconfigurability of the OLMCs, managed through a dedicated architecture control word, is what allowed a single GAL18V10B to replace a wide variety of fixed-function PALs and simple discrete logic chips.

Key Features and Specifications

The "10LJ" suffix provides specific details about the device's performance and packaging:

-10: Indicates a maximum propagation delay of 10 ns, making it a high-speed solution for its era.

LJ: Denotes a 20-pin Plastic Leaded Chip Carrier (PLCC) package.

Other critical features include:

Electrically Erasable (EE) CMOS Technology: Unlike OTP PALs, the GAL18V10B could be erased and reprogrammed thousands of times, drastically accelerating design development and prototyping.

100% Testability: The architecture supported functional testing, ensuring high reliability.

Low Power Consumption: Utilizing CMOS technology resulted in significantly lower power draw than bipolar PAL alternatives.

Key Applications

The GAL18V10B-10LJ found widespread use as a "glue logic" component, integrating multiple discrete digital ICs into a single, programmable chip. Its primary applications included:

Address Decoding: In microprocessor and microcontroller-based systems, it was ideal for generating chip select signals from address buses.

State Machine Design: Its registered outputs made it perfect for implementing finite state machines (FSMs) for control logic.

Bus Interface Logic: It was commonly used for implementing interface protocols and timing between different parts of a system.

Code Conversion and Data Multiplexing: It efficiently replaced multiple simple logic gates (AND, OR, NOT) for data routing and conversion tasks.

ICGOODFIND Summary: The Lattice GAL18V10B-10LJ was a revolutionary device that democratized programmable logic. Its reprogrammable CMOS technology, configurable macro-cells, and high speed made it an indispensable tool for engineers, consolidating complex TTL logic into a single, reliable, and fast chip. It paved the way for the larger and more complex CPLDs and FPGAs that followed.

Keywords:

Programmable Logic Device (PLD)

Generic Array Logic (GAL)

Output Logic Macro Cell (OLMC)

Glue Logic

Finite State Machine (FSM)