Lattice GAL16V8D-10LPI: An In-Depth Technical Overview and Application Guide
The Lattice GAL16V8D-10LPI stands as a seminal device in the history of programmable logic. As a member of the Generic Array Logic (GAL) family, it provided a powerful, erasable, and electrically erasable (EEPROM) alternative to once-programmable PAL devices, revolutionizing digital design prototyping and low-to-medium volume production. This article delves into the technical specifications, architecture, and practical applications of this iconic component.
Architectural Breakdown
At its core, the GAL16V8D-10LPI is a 20-pin, low-power industrial-grade PLD. The nomenclature "16V8" is descriptive: it has up to 16 dedicated inputs and 8 output logic macrocells, capable of generating 8 outputs. Its programmability is based on a sum-of-products (SOP) logic structure.
The key to its flexibility lies in its Output Logic Macrocell (OLMC). Each of the eight macrocells can be individually configured by the user-defined fuse map to operate in several modes:
Combinational (Simple) Mode: The output is solely a function of the input and product-term array.
Registered Mode: The output is passed through a D-type flip-flop, synchronizing the output to the clock signal. This is crucial for implementing state machines and synchronous counters.
Complex Mode: Allows for feedback paths, where an output can be fed back into the logic array as an input, enabling more complex logic functions.
This reconfigurable macrocell architecture was a significant advancement, allowing a single, standard chip to implement a vast array of logic functions.
Decoding the Part Number: GAL16V8D-10LPI
GAL: Generic Array Logic.
16V8: 16 inputs, 8 outputs.
D: Indicates the specific variant (often related to package or technology revision).
-10: The maximum propagation delay (tPD) is 10 ns, defining its speed grade. A lower number indicates a faster device.
LPI: Low Power, Industrial temperature grade. This signifies it operates over the industrial temperature range (-40°C to +85°C) with lower power consumption compared to standard parts.
Key Features and Specifications
Technology: EEPROM-based cell configuration. Non-volatile and reprogrammable, offering over 100 erase/write cycles.
Speed: 10 ns maximum propagation delay.
Power: Low-power CMOS technology.
Package: 20-pin PDIP (Plastic Dual In-line Package), as denoted by the package code in the full part number.
Logic Capacity: 64 product terms.
Application Guide
The GAL16V8D-10LPI was designed to consolidate multiple standard TTL logic chips (e.g., 74-series) into a single, customizable device. Its primary applications included:
1. Address Decoding: Generating chip select (CS) signals in microprocessor/microcontroller systems.
2. State Machine Design: Implementing finite state machines (FSMs) for control logic, utilizing its registered output mode.
3. Bus Interface Logic: Creating glue logic for interfacing between components with different protocols or timing requirements.
4. Code Conversion and Data Gating: Implementing simple combinational functions like encoders, decoders, and multiplexers.
Design Flow:
1. Logic Definition: Define the desired logic function using truth tables, state diagrams, or Boolean equations.
2. Design Entry: Use a Hardware Description Language (HDL) like VHDL or Verilog, or more traditionally, schematic entry or Boolean equations in a PLD development tool.
3. Compilation & Fuse Map Generation: The software compiler (e.g., CUPL, Abel) translates the design into a JEDEC file, which contains the fuse map for programming.
4. Programming: A dedicated GAL programmer is used to electrically erase and program the device with the JEDEC file.
5. Testing: The programmed device is inserted into the target circuit for verification and testing.
While the GAL16V8D-10LPI is a legacy device, its impact is undeniable. It served as a critical bridge between fixed TTL logic and modern high-density FPGAs and CPLDs. For engineers today, understanding its architecture provides fundamental insights into programmable logic design principles. For legacy system maintenance and repair, sourcing a reliable GAL programmer and understanding the JEDEC fuse map remain essential. It represents a pivotal moment in electronics, embodying the shift towards in-system programmability and hardware flexibility.
Keywords:
GAL (Generic Array Logic)
Programmable Logic Device (PLD)
Output Logic Macrocell (OLMC)
JEDEC File
Propagation Delay (tPD)
