Lattice GAL22V10C-10LJ: Architecture, Features, and Key Applications in Digital Logic Design
The Lattice GAL22V10C-10LJ stands as a quintessential and highly influential 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 architecture and flexibility made it a cornerstone for prototyping, education, and medium-complexity digital designs throughout the 1980s and 1990s.
Architecture: A Look Inside
The "22V10" nomenclature is descriptive of its core architecture. The device features 22 input pins, with 10 of the output pins configured as programmable I/O macrocells. This macrocell-based architecture is the key to its versatility. Each of the 10 output macrocells can be individually configured by the user through a process of electrical programming and erasure (using UV light or, in later versions, electrically).
The internal logic consists of a programmable AND array followed by a fixed OR array. The user-defined AND terms feed into the OR array, which then connects to the sophisticated output macrocell. Each macrocell can be programmed for various output configurations, including combinatorial output, registered (clocked) output, and bidirectional I/O. Crucially, the macrocell also controls the output polarity (active-high or active-low), simplifying the implementation of complex logic functions.
Salient Features
The GAL22V10C-10LJ boasts several defining features that cemented its popularity:
High Flexibility: The programmable macrocell structure allows it to emulate a wide range of fixed-function logic devices, from simple gates to counters and state machines.
Reusability: Unlike one-time programmable (OTP) parts, the erasable (UV or EEPROM) nature of the GAL22V10 allowed for design iteration and correction, drastically reducing development time and cost.
Full Programmability of Outputs: The ability to configure each output as combinatorial or registered provided immense design freedom.
-10LJ Speed Grade: The "-10" suffix indicates a maximum pin-to-pin propagation delay of 10 nanoseconds, making it suitable for moderately high-speed logic applications. The "LJ" denotes a 28-pin PLCC (Plastic Leaded Chip Carrier) package.
Low Power Consumption: Compared to implementing the same function with a board full of TTL chips, a single GAL device offered a significant reduction in power consumption and board space.
Key Applications in Digital Logic Design
The GAL22V10 found its way into countless applications, serving as a universal glue logic and system integration component.
State Machine Implementation: It was exceptionally well-suited for implementing finite state machines (FSMs). The registered macrocells were perfect for storing the current state, while the combinatorial logic could define the next state and outputs.
Address Decoding: In microprocessor-based systems, it was ideal for generating complex chip-select and memory-mapped I/O decoding signals from the address bus.
Bus Interface Logic: It was commonly used to implement interface protocols, data latches, and buffers for connecting peripherals to a central bus.
Function Emulation: A single GAL could replace dozens of simple TTL gates (AND, OR, NOT, flip-flops), leading to more reliable, compact, and power-efficient printed circuit boards (PCBs).
Prototyping and Education: Its re-programmability made it an invaluable tool for teaching digital logic concepts and for prototyping designs before committing to an ASIC or more complex PLD.
The Lattice GAL22V10C-10LJ is a legendary device that democratized digital design. Its macrocell-based architecture provided an unprecedented blend of flexibility, speed, and reusability for its time. It served as a critical bridge between discrete logic and the high-density FPGAs and CPLDs of today, teaching a generation of engineers the power of programmable logic.
Keywords:
1. Programmable Logic Device (PLD)
2. Output Macrocell
3. Generic Array Logic (GAL)
4. Finite State Machine (FSM)
5. Glue Logic
