Programming and Applications of the Lattice GAL16V8C-15LJ CPLD
The Lattice GAL16V8C-15LJ stands as a classic and highly influential device in the realm of digital logic design. As a Generic Array Logic (GAL) device, it belongs to the broader category of Complex Programmable Logic Devices (CPLDs). Its enduring popularity, even in an era dominated by FPGAs, is a testament to its simplicity, reliability, and cost-effectiveness for solving a vast array of glue logic and combinatorial problems.
Architectural Overview
The GAL16V8C-15LJ's architecture is elegantly straightforward. The "16" indicates it has up to 16 inputs, while the "8" denotes up to 8 outputs. These I/O pins are bidirectional, providing significant design flexibility. The core of the device consists of a programmable AND array feeding into fixed OR arrays. This structure allows designers to create a wide variety of sum-of-products logic functions.
A key feature of the GAL architecture is its Output Logic Macrocell (OLMC). Each of the eight outputs is controlled by a macrocell that can be configured by the user for various modes of operation, including combinatorial output, registered (clocked) output, or as a dedicated input. The "-15" in its part number specifies a maximum pin-to-pin propagation delay of 15 nanoseconds, making it suitable for moderately high-speed applications.
Programming Paradigm
Programming the GAL16V8C-15LJ is a well-established process. It is typically accomplished using a hardware programmer and software tools that convert a user's logic design into a JEDEC file (a standard format for programming PLDs). The process involves:
1. Design Entry: The desired logic function is described using Boolean equations, schematic capture, or a Hardware Description Language (HDL) like VHDL or Verilog. For simpler designs, Boolean equations are often the most direct method.
2. Compilation and Fit: The software tool compiles the design, minimizes the logic, and fits it into the device's resources, generating the JEDEC file.
3. Programming: The JEDEC file is transferred to a dedicated hardware programmer, which applies the necessary voltages and signals to configure the device's internal Erasable CMOS (E²CMOS) cells. This technology allows the device to be erased and reprogrammed multiple times, facilitating design iteration and debugging.
Key Application Areas
The GAL16V8C-15LJ excels in applications where a handful of standard logic ICs (like the 7400-series) would otherwise be required. Its primary value lies in system integration, reducing board space, component count, and power consumption.
Address Decoding: It is perfectly suited for generating chip select (CS) and read/write signals in microprocessor and microcontroller-based systems, decoding specific address ranges from the address bus.
State Machine Control: While limited in complexity compared to larger CPLDs or FPGAs, it is highly effective for implementing simple finite state machines (FSMs) for control logic, interface management, and sequence generation.
Bus Interface and Glue Logic: It is ideal for bridging logic level differences, signal gating, and creating custom timing and control signals between different subsystems or ICs on a PCB (e.g., between a CPU and memory or peripherals).
I/O Expansion and Port Control: It can be used to manage and decode signals for I/O port expansion, reducing the load on a main processor.
Advantages and Considerations
The primary advantage of the GAL16V8C-15LJ is its simplicity and low cost. Designs are quick to implement, and the device is incredibly robust for its intended purposes. Its deterministic timing, inherent to CPLD architecture, is a significant benefit over FPGAs for simple, timing-critical glue logic.
However, its limitations are clear: a limited logic capacity and a relatively small number of macrocells make it unsuitable for complex designs. For larger projects, modern CPLDs or FPGAs offer far greater density and features.
ICGOODFIND Summary: The Lattice GAL16V8C-15LJ CPLD remains a fundamental and powerful tool for digital designers. It embodies the principle of efficient logic integration, offering a perfect blend of programmability, performance, and price for a vast range of "glue logic" applications. Its role in educating engineers on PLD concepts and its continued use in industrial control, consumer electronics, and communications hardware solidify its status as a timeless component in the world of programmable logic.
Keywords:
1. Programmable Logic Device (PLD)
2. Output Logic Macrocell (OLMC)
3. JEDEC File
4. Address Decoding
5. Glue Logic
