Lattice GAL16V8B-10LJ: Architecture, Programming, and Application in Digital Logic Design

The Lattice GAL16V8B-10LJ stands as a quintessential example of a Generic Array Logic (GAL) device, a pioneering technology that helped bridge the gap between expensive, custom-masked PALs and the inflexibility of standard logic ICs. This particular device, with its 10ns maximum propagation delay, became a workhorse for implementing complex combinational and sequential logic in late 20th-century digital designs, offering a reprogrammable and cost-effective solution.

Architecture of the GAL16V8B

The architecture of the GAL16V8B is a masterpiece of programmable logic design, centered around a highly configurable AND-OR structure. The "16V8" nomenclature is descriptive: it has up to 16 inputs and 8 outputs. Its core components include:

Programmable AND Array: This is the primary logic engine. It consists of a grid of fusible links that allow any input or its complement to be connected to any product term (AND operation). The array accepts inputs from the dedicated input pins and feedback paths from the output macrocells.

Fixed OR Array: Unlike its PAL predecessors, which had a fixed number of product terms per output, the GAL16V8 features a fixed OR array that sums a specific set of product terms for each output macrocell. This structure provides a predictable logic resource allocation.

Output Logic Macrocell (OLMC): This is the most critical and innovative feature. Each of the eight outputs is driven by a configurable OLMC. The OLMC contains a D-type flip-flop and multiplexers that allow each pin to be configured as:

A dedicated input.

A combinatorial output (active high or active low).

A registered output (active high or active low).

A bidirectional I/O pin.

This extreme flexibility allows the same silicon device to implement a vast range of logic functions, from simple decoders to state machines.

Programming the Device

Programming the GAL16V8B-10LJ is a process of configuring the AND array and the OLMCs to realize a specific Boolean logic function. The process involves several key steps:

1. Logic Design & Description: The desired logic function is described using Boolean equations, a state diagram, or a schematic. This is the functional specification.

2. Compilation (JEDEC File Generation): The design is entered into a software tool, originally often CUPL or Abel, and modernly supported by some open-source tools. The compiler translates the logic into a fuse map – a precise pattern of which links in the AND array to "blow" (leave open) and which to leave intact. This map is saved in a standard JEDEC file format.

3. Device Programming: A dedicated GAL programmer (or universal programmer configured for this device) is used. The programmer erases any previous configuration and then electrically programs the device by applying specific voltage pulses to set the internal EEPROM cells (which replaced the original one-time programmable fuses) according to the JEDEC file. The `-10LJ` suffix indicates a 10ns speed grade and a plastic leaded chip carrier (PLCC) package.

Application in Digital Logic Design

The GAL16V8B found widespread application as a universal "glue logic" component. Its ability to replace multiple simple ICs (like the 7400-series) with a single, programmable chip was revolutionary. Key applications included:

Address Decoding: Generating chip select (CS) signals for microprocessors and memory systems.

State Machine Implementation: Creating finite state machines for control logic, with the internal flip-flops storing the current state.

Bus Interface Logic: Implementing custom timing and control signals for interfacing between different digital subsystems.

Code Converters and Pattern Generators: Performing combinatorial logic operations like converting between binary and Gray code.

Its reprogrammability was its greatest asset, allowing for rapid design iteration and bug fixes without the need to fabricate new hardware, dramatically accelerating prototyping and development cycles.

ICGOOODFIND: The Lattice GAL16V8B-10LJ was a foundational pillar in the evolution of programmable logic. It democratized digital design by offering a low-cost, flexible, and sufficiently powerful solution that empowered engineers to consolidate complex logic onto a single chip. While modern CPLDs and FPGAs have vastly surpassed its capacity and speed, the architectural concepts of the programmable AND array and configurable macrocell, perfected in devices like the GAL16V8, remain at the heart of logic design today.

Keywords: Programmable Logic Device (PLD), Generic Array Logic (GAL), Output Logic Macrocell (OLMC), JEDEC File, Digital Glue Logic