Lattice GAL16V8D-5LJ: Architecture, Programming, and Application in Digital Logic Design
The Lattice GAL16V8D-5LJ 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 reconfigurable alternative to fixed-function TTL logic and one-time programmable PAL devices. Its impact on digital logic design, particularly in prototyping and medium-complexity state machine implementation, remains significant.
Architecture of the GAL16V8D-5LJ
The architecture of the GAL16V8 is ingeniously designed around a programmable AND array feeding into a fixed OR array. This structure efficiently implements sum-of-products (SOP) logic functions. The "16V8" designation reveals its core configuration: it has up to 16 inputs, 8 outputs, and a maximum of 8 product terms per output.
A key architectural innovation is the Output Logic Macrocell (OLMC). Each of the eight outputs is driven by a configurable OLMC, which provides tremendous flexibility. Through programming, each OLMC can be configured as:
A dedicated combinatorial output (active high or low).
A dedicated input.
A registered output (with a D-type flip-flop) for implementing sequential logic like counters and state machines.
A combinatorial I/O pin whose direction can be controlled.
This macrocells are the cornerstone of the device's versatility. The "-5LJ" suffix specifically denotes a 5ns maximum propagation delay (tPD) and a 20-pin PLCC (Plastic Leaded Chip Carrier) package.
Programming the Device
Programming the GAL16V8D-5LJ is a process of defining the connections within its programmable AND array. Engineers write Boolean equations or create state machine diagrams describing the desired logic. These are then processed by a software tool called a compiler (e.g., CUPL, WinCUPL, or Abel), which translates the high-level logic into a standard JEDEC file.
This JEDEC file, containing a map of which fuses to "blow" (disconnect), is physically transferred to the blank GAL device using a dedicated GAL programmer. A critical advantage of the GAL16V8D-5LJ over its PAL predecessors is its use of EEPROM (Electrically Erasable Programmable Read-Only Memory) technology. This allows the device to be erased electrically and reprogrammed thousands of times, making design iteration and debugging vastly more efficient.
Application in Digital Logic Design
The primary application of the GAL16V8D-5LJ was to consolidate multiple simple TTL chips (e.g., 74LS series gates, flip-flops, decoders) into a single, compact chip. This led to significant benefits:
Reduced Board Space: Replacing several ICs with one.
Increased Reliability: Fewer physical interconnections and components.
Design Security: The programmed logic function is difficult to reverse-engineer.
Rapid Prototyping: Logic could be designed, tested, and modified quickly without changing PCB traces.
It was exceptionally well-suited for implementing glue logic (address decoding, bus interfacing), combinational functions, and finite state machines of moderate complexity. Its 5ns speed rating made it applicable for high-performance systems where fast propagation was critical.
In summary, the Lattice GAL16V8D-5LJ was a revolutionary programmable logic device that democratized digital design. Its reprogrammable EEPROM technology and highly flexible Output Logic Macrocell (OLMC) architecture empowered engineers to create complex, customizable logic circuits with unprecedented speed and efficiency. It served as a vital bridge between discrete logic and the more complex FPGAs and CPLDs that followed, cementing its legacy as a foundational component in electronics development.
Keywords:
1. Programmable Logic Device (PLD)
2. Output Logic Macrocell (OLMC)
3. EEPROM Technology
4. JEDEC File
5. Sum-of-Products (SOP)
