Lattice GAL26CV12B-20LJ: A Comprehensive Technical Overview of the 20ns PLD

The Lattice GAL26CV12B-20LJ represents a pivotal component in the history of programmable logic, offering a blend of high performance and design flexibility that was instrumental in countless digital systems. As a member of the Generic Array Logic (GAL) family, this device is an electrically erasable (EE) programmable logic device (PLD) that provided a powerful, yet cost-effective, solution for integrating complex combinational and sequential logic.

Architectural Foundation

At its core, the GAL26CV12B-20LJ features a programmable AND array feeding into a fixed OR array. This classic PLD architecture is combined with 12 output logic macro cells (OLMCs), which are a key to its versatility. The "26" denotes the number of inputs, while the "12" indicates the number of outputs. Each OLMC can be individually configured for combinatorial or registered operation, with programmable output polarity (active-high or active-low) and control over the output enable. This flexibility allows the device to implement a wide range of logic functions, from simple glue logic to more complex state machines.

Key Performance Specifications

The "-20LJ" suffix is critical, specifying both the speed grade and the package. The 20ns maximum propagation delay (tPD) from any input to any output ensured high-speed operation for its era, making it suitable for performance-critical applications. The "LJ" denotes a 28-pin Plastic Leaded Chip Carrier (PLCC) package, a common surface-mount format that facilitated compact PCB design. The device operates on a standard 5V power supply, consistent with the technology of its time.

In-System Programmability and Reusability

A significant advantage over its PAL predecessors was its use of Electrically Erasable (E2) CMOS technology. This allowed the device to be reprogrammed thousands of times, drastically accelerating the design iteration and debugging process. Engineers could revise logic designs in-system without physically removing the chip, a feature that streamlined development cycles and reduced costs.

Design and Application

Development for the GAL26CV12B-20LJ was typically done using Hardware Description Languages (HDLs) like ABEL or CUPL, or schematic entry tools. These tools generated a JEDEC file that was used to program the device. Its primary applications were vast, including:

Address decoding in microprocessor and memory systems.

Bus interface and control logic.

State machine implementation.

Replacing multiple standard TTL logic chips, reducing board space, power consumption, and improving system reliability.

Legacy and Modern Context

While modern Complex Programmable Logic Devices (CPLDs) and Field-Programmable Gate Arrays (FPGAs) have far surpassed the density and performance of the GAL26CV12B, its legacy is profound. It served as a fundamental building block, teaching a generation of engineers the principles of programmable logic and enabling the rapid digital system development that defined the late 80s and 90s.

ICGOODFIND: The Lattice GAL26CV12B-20LJ stands as a quintessential high-performance PLD, renowned for its 20ns speed, 12 reconfigurable macro cells, and electrically erasable technology. It was a cornerstone for logic integration, embodying the shift towards flexible, software-defined hardware.

Keywords: Programmable Logic Device (PLD), Electrically Erasable (E2CMOS), 20ns Propagation Delay, Output Logic Macro Cell (OLMC), Programmable AND Array