A Comprehensive Guide to the Lattice GAL22V10D-15LP Programmable Logic Device

In the realm of digital logic design, Programmable Logic Devices (PLDs) have served as the fundamental building blocks for countless electronic systems. Among these, the Generic Array Logic (GAL) family from Lattice Semiconductor stands out for its innovation, particularly the GAL22V10D-15LP, which became a workhorse for prototyping, education, and medium-complexity logic implementations. This guide provides a comprehensive overview of this iconic device.

Architecture and Core Features

The GAL22V10D is an electrically erasable, CMOS-based PLD. Its name reveals its key characteristics: 22 inputs, 10 output logic macrocells (OLMCs), and a D-type register configuration. The -15LP suffix denotes a 15ns maximum propagation delay and Low Power CMOS technology, making it a balance of speed and efficiency for its era.

Its architecture is centered around a programmable AND array feeding into a fixed OR array. The heart of its flexibility lies in its Output Logic Macrocell (OLMC). Each of the ten outputs can be individually configured by the user to be:

Combinational: Either active-high or active-low.

Registered: Utilizing a D-type flip-flop for synchronous, clocked operations.

Programmable I/O: Pins can be defined as inputs or outputs, maximizing the use of available pins.

This macrocell versatility allowed designers to implement a wide variety of logic functions, including state machines, counters, decoders, and address translators, all within a single, compact chip.

Key Programming and Design Flow

Programming the GAL22V10D requires a GAL programmer and a logic compiler. The design process typically follows these steps:

1. Logic Definition: The desired function is defined using Boolean equations, state diagrams, or a schematic.

2. Compilation: The design is entered into a software tool (e.g., CUPL, Abel) which compiles the logic into a JEDEC file (a standard fuse map file).

3. Programming: The JEDEC file is transferred to a hardware programmer, which electrically configures the internal floating-gate cells of the GAL device.

4. Verification: The programmed device can be tested in-circuit or with a verification fixture.

A critical advantage of the GAL22V10D over its predecessor, the PAL, is its reprogrammability. This allowed for rapid design iteration and bug fixes without discarding hardware.

Applications and Legacy

The GAL22V10D-15LP found extensive use in numerous applications:

Address Decoding: In microprocessor-based systems, it was perfect for generating chip-select signals.

Glue Logic: It excelled at replacing multiple small- and medium-scale integration (SSI/MSI) ICs, reducing board space, power consumption, and part count.

Interface Logic: For converting between different logic levels or protocols.

State Machine Control: Implementing simple control sequences and timing logic.

While modern Complex PLDs (CPLDs) and FPGAs have largely superseded simple PLDs for new designs, the GAL22V10D remains a legendary device. It demonstrated the power of in-system programmability and paved the way for more complex programmable logic. It is still revered for teaching the core concepts of programmable logic and for maintaining legacy equipment.

ICGOODFIND: For engineers and hobbyists working with 1990s and early 2000s technology, or for those learning the fundamentals of digital hardware design, the Lattice GAL22V10D-15LP remains an ICGOODFIND. Its perfect blend of simplicity, flexibility, and reliability makes it an enduring solution for replacing hardwired logic and understanding the roots of programmable logic.

Keywords: Programmable Logic Device, Output Logic Macrocell (OLMC), JEDEC File, Reprogrammable, Glue Logic