Lattice GAL16V8C-5LJ: Architecture, Programming, and Application in Digital Logic Design
The Lattice GAL16V8C-5LJ stands as a seminal device in the history of programmable logic, representing a highly popular and influential Generic Array Logic (GAL) device. As an electrically erasable programmable logic device (EEPROM-based PLD), it offered a reusable and flexible alternative to fixed-function TTL logic and one-time programmable PAL devices, revolutionizing prototyping and digital system design in the late 1980s and 1990s.
Architecture of the GAL16V8C-5LJ
The part number "GAL16V8" itself is descriptive of its core architecture. The "16" indicates the number of dedicated inputs, while the "8" refers to the maximum number of outputs. The "V" signifies a versatile output structure. The specific suffix "C-5LJ" denotes a commercial-grade device with a 5ns maximum propagation delay, in a PLCC-20 package.
Its internal architecture is centered around a programmable AND array feeding into fixed OR arrays and sophisticated Output Logic Macro Cells (OLMCs). The AND array is the primary programmable element, creating product terms from the input signals. The true innovation of the GAL device lies in its OLMCs. Each of the eight outputs can be individually configured by the designer to operate in various modes:
Combinational Output: A simple active-high or active-low output from the AND-OR array.
Registered Output: The output is passed through a D-type flip-flop, essential for implementing state machines and synchronous sequential logic.
Combinational I/O: The pin can act as an additional input, with the output being disabled.
This reconfigurability is what made the GAL16V8C-5LJ vastly more versatile than its predecessors.
Programming the Device
Programming the GAL16V8C-5LJ is a well-defined process. A designer first creates a logic design using Boolean equations, a state diagram, or a schematic. This design is then entered into a Hardware Description Language (HDL) like CUPL or Abel, which were standard for these devices. The HDL compiler translates the design into a JEDEC file – a standard file format containing the fuse map information.
This JEDEC file is then transferred to a dedicated GAL programmer (or universal programmer). The programmer applies a higher voltage to the device, electrically burning (or, more accurately, charging) the floating gates in the EEPROM-based AND array to create the desired circuit connections. The "electrically erasable" feature meant the device could be erased with UV light or electrically (depending on the technology) and reprogrammed thousands of times, making design iteration rapid and cost-effective.
Application in Digital Logic Design
The primary application of the GAL16V8C-5LJ was to integrate multiple simple TTL chips (such as the 7400-series) into a single, compact package. This led to significant benefits:
Reduced Board Space: Replacing several SSI/MSI chips with one 20-pin IC.
Increased Reliability: Fewer physical interconnections and components lowered failure rates.
Design Security: The programmed function was difficult to reverse-engineer.
Faster Time-to-Market: Logic could be changed in software and reprogrammed without altering the PCB layout.
Common applications included:
Address Decoding: In microprocessor systems to generate chip select signals.
State Machine Control: Implementing control logic for sequencers and controllers.
Glue Logic: Interfacing between larger integrated circuits with different signaling standards.
Bus Interface Logic: Implementing custom timing and handshaking protocols.
While modern Complex PLDs (CPLDs) and FPGAs have largely superseded simple GALs for new designs, the GAL16V8C-5LJ remains a classic tool for teaching fundamental digital logic concepts and for maintaining legacy electronic systems.
The Lattice GAL16V8C-5LJ was a cornerstone of digital logic design, providing an unparalleled combination of flexibility, density, and reprogrammability for its era. Its innovative Output Logic Macro Cell (OLMC) architecture empowered designers to consolidate complex logic functions, paving the way for the high-density programmable logic devices we rely on today.
Keywords:
1. Programmable Logic Device (PLD)
2. Generic Array Logic (GAL)
3. Output Logic Macro Cell (OLMC)
4. JEDEC File
5. Hardware Description Language (HDL)
