Lattice GAL16V8D-10LJI: Architecture, Features, and Application Circuit Design

The Lattice GAL16V8D-10LJI stands as a quintessential example of a high-performance, low-power programmable logic device (PLD) from the Generic Array Logic (GAL) family. As a 20-pin, electrically erasable CMOS device, it offers designers a flexible and reliable solution for implementing complex combinatorial and sequential logic functions, serving as a hardware-agnostic alternative to multiple discrete logic ICs.

Architectural Overview

At its core, the GAL16V8D-10LJI architecture is built around a programmable AND array feeding into a fixed OR array. This structure effectively creates a sum-of-products logic engine. The device features eight logic macro cells, each associated with an input/output (I/O) pin. Each macrocell can be configured by the user to operate in various modes: combinatorial, registered, or complex I/O, providing immense design flexibility. The internal logic is structured such that it can emulate a wide range of standard logic gates, decoders, multiplexers, and state machines. The `-10` in its part number signifies a maximum pin-to-pin propagation delay of 10ns, making it suitable for moderately high-speed applications.

Key Features

The GAL16V8D-10LJI is characterized by several defining features:

High Performance: A maximum operating frequency of 62.5 MHz and a 10ns maximum propagation delay enable its use in timing-critical circuits.

Low Power Consumption: Fabricated in advanced CMOS technology, it consumes significantly less power than its bipolar (e.g., PAL) predecessors.

Electrically Erasable: The E²CMOS (Electrically Erasable CMOS) technology allows the device to be reprogrammed and tested repeatedly, drastically accelerating the development cycle and reducing time-to-market.

100% Testability: The programmable architecture ensures that all internal logic functions can be fully verified, guaranteeing high manufacturing yields and design reliability.

High Output Drive: With an output current of 24mA, it can drive relatively high capacitive loads and directly interface with system buses without requiring additional buffers.

Application Circuit Design

A typical application circuit for the GAL16V8D-10LJI involves using it as a glue logic controller or a state machine. Consider a design where it functions as an address decoder and a data routing multiplexer in a microprocessor-based system.

1. Circuit Function: The PLD is tasked with generating chip select (CS) signals for various memory (RAM, ROM) and peripheral ICs based on the upper bits of the address bus (A15-A12). Simultaneously, it controls a bidirectional data buffer based on the system's Read/Write (R/W) signal.

2. Design Implementation:

The microprocessor's address lines A15-A12 are connected to four dedicated input pins on the GAL16V8D.

The R/W signal is connected to another input pin.

The output pins of the GAL are configured to generate the active-low chip select signals (`/CS_RAM`, `/CS_ROM`, `/CS_PERIPH`).

Another output pin is configured to generate the output enable (`OE`) signal for the data buffer, activated under specific address and R/W conditions.

3. Programming: The desired logic functions (the truth table for decoding addresses and controlling the buffer) are written in a Hardware Description Language (HDL) like VHDL or Verilog, or more traditionally, entered as Boolean equations or a schematic. This design is then compiled into a standard JEDEC file. Using a universal programmer, this JEDEC file is fused into the GAL16V8D-10LJI, configuring its internal AND-OR logic arrays to perform the exact required function.

4. Power and Clock: The `VCC` (pin 20) is connected to a stable +5V supply, and `GND` (pin 10) is connected to ground. A global clock signal (if using registered mode) is applied to pin 1. Bypass capacitors (0.1µF ceramic) must be placed close to the power pins to ensure stable operation and suppress switching noise.

ICGOOODFIND

The Lattice GAL16V8D-10LJI remains a valuable component for engineers seeking a simple, fast, and cost-effective solution for integrating discrete logic. Its reprogrammability offers a significant advantage over fixed-function ICs, making it ideal for prototyping, reducing board space, and implementing last-minute logic changes without altering the physical PCB. It perfectly bridges the gap between standard logic and more complex FPGAs/CPLDs.

Keywords: Programmable Logic Device (PLD), Electrically Erasable CMOS (E²CMOS), Macrocell, Glue Logic, Propagation Delay.