Lattice GAL22V10D-15LPI: Architecture, Key Features, and Target Applications

The Lattice GAL22V10D-15LPI 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, consolidating logic design and accelerating development cycles. Its architecture, performance, and reliability made it a cornerstone in countless electronic systems from the late 1980s through the early 2000s.

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 that feeds a fixed OR array. This structure allows designers to create a wide variety of combinatorial and sequential logic functions.

The heart of its flexibility lies in the Output Logic Macrocell (OLMC). Each macrocell can be individually configured by the user to control the output's behavior, including:

Combinatorial or Registered Output: The output can be a direct result of the logic operation (combinatorial) or stored in a D-type flip-flop (registered) for implementing state machines and counters.

Output Polarity: The output sense (active-high or active-low) can be programmed.

Tri-State Control: Each output can be put into a high-impedance state, enabling bus-oriented applications.

This macrocell architecture was revolutionary, as a single GAL device could replace numerous fixed-function PALs or simple TTL logic chips, drastically reducing board space and part count.

Key Features and Specifications

The GAL22V10D-15LPI's specifications define its capabilities and performance envelope:

High-Speed Performance: The -15LJ suffix indicates a maximum propagation delay of 15 nanoseconds, making it suitable for high-speed logic applications.

Electrically Erasable (EE) CMOS Technology: Unlike one-time programmable (OTP) PALs, the GAL22V10D uses EECMOS technology. This allows the device to be reprogrammed and erased thousands of times, facilitating design iteration, debugging, and prototyping.

Low Power Consumption: Built on CMOS technology, it consumes significantly less power than bipolar PAL equivalents.

100% Testability: The logic functions could be thoroughly tested and verified during manufacturing.

Security Fuse: A programmable security bit prevents the internal pattern from being read back, protecting intellectual property from competitors.

Target Applications

The versatility of the GAL22V10D-15LPI made it a ubiquitous component across numerous industries. Its primary role was to integrate and glue together more complex subsystems. Key application areas included:

Address Decoding: Generating chip-select signals for microprocessors (e.g., 68000, Z80, x86) in computer and embedded systems.

State Machine Design: Implementing finite state machines (FSMs) for control logic and sequencers.

Bus Interface Logic: Acting as an interface between components with different timing or protocol requirements.

I/O Port Expansion and Control: Managing input/output functions in microcontroller-based systems.

Digital Signal Conditioning: Performing simple logic operations like multiplexing, demultiplexing, and encoding/decoding.

While largely superseded by larger CPLDs and FPGAs today, the GAL22V10D was instrumental in demonstrating the power and cost-effectiveness of programmable logic, paving the way for modern digital design.

ICGOODFIND: The Lattice GAL22V10D-15LPI was a foundational workhorse of programmable logic. Its reprogrammable macrocell-based architecture offered unprecedented flexibility for integrating "glue logic," enabling simpler PCB designs, faster time-to-market, and reduced system cost across a vast range of digital applications from the 1980s to the early 2000s.

Keywords:

Programmable Logic Device (PLD)

Generic Array Logic (GAL)

Output Logic Macrocell (OLMC)

Glue Logic

Finite State Machine (FSM)