Lattice GAL22V10D-10LJN: Architecture, Features, and Application Design Considerations
The Lattice GAL22V10D-10LJN represents a classic yet enduringly relevant component in the realm of digital logic design. As a member of the Generic Array Logic (GAL) family, this device offers a versatile and reliable platform for implementing a wide array of combinatorial and sequential logic functions. Its architecture, a precursor to more complex CPLDs and FPGAs, remains a fundamental building block for many embedded systems, particularly where simplicity, cost-effectiveness, and low power consumption are paramount.
Architecture: A Look Inside
The core architecture of the GAL22V10D is a programmable AND array feeding into a fixed OR array, a structure known as a Programmable Logic Device (PLD). The "22V10" designation is key to understanding its capabilities:
22 Inputs: The device features up to 22 dedicated inputs.
10 Outputs: It provides 10 output logic macrocells (OLMCs), which are the cornerstone of its flexibility.
Programmable AND Array: This is the fusible link matrix that allows designers to define custom product terms (minterms) for their logic functions. The inputs and their complements are fed into this array, which can be programmed to create the necessary logic combinations.
The most critical architectural element is the Output Logic Macrocell (OLMC). Each of the ten outputs is controlled by its own macrocell, which can be individually configured. Key configuration options include:
Programmable Polarity: A XOR gate at the output allows each pin to be configured as either active-high or active-low, simplifying logic design.
Output Registering: Each macrocell contains a D-type flip-flop that can be used to register the output, enabling the implementation of state machines and synchronous sequential circuits.
Feedback Paths: The registered output can be fed back into the AND array, allowing the current state to be used for calculating the next state.
I/O Control: Macrocells can be configured as dedicated inputs, dedicated combinatorial outputs, or registered outputs.
Key Features and Specifications
The GAL22V10D-10LJN variant comes with a specific set of characteristics that define its performance:
High-Speed Operation: The `-10` suffix denotes a maximum pin-to-pin propagation delay of 10 ns, making it suitable for moderately high-speed applications.
Low Power Consumption: Fabricated in CMOS technology, it features low power dissipation, both in active and standby modes, which is ideal for power-sensitive designs.
Erasable and Reprogrammable: Unlike one-time programmable PALs, the GAL family uses an EEPROM-based technology. This allows the device to be erased and reprogrammed hundreds of times, significantly accelerating prototyping and design iteration.
100% Testability: The architecture supports JEDEC-standard functional test vectors, ensuring high reliability and manufacturability.
Package: The `LJN` suffix indicates a 28-pin Plastic Leaded Chip Carrier (PLCC) package, a common through-hole and socket-mountable form factor.
Application Design Considerations
Successfully integrating the GAL22V10D into a design requires careful consideration of several factors:
1. Logic Capacity: While versatile, the device has a finite number of product terms per output (ranging from 8 to 16). Designers must ensure their logic equations fit within these constraints. Logic minimization techniques are crucial for efficient utilization.
2. Clock and Reset Planning: As a synchronous device, careful attention must be paid to the global clock and output enable signals. The clock-to-output time (tCO) is a critical parameter for timing analysis in sequential designs. A global asynchronous reset is available for initializing all registers.
3. Pinout and I/O Configuration: Strategically assigning signals to pins can minimize internal routing congestion and improve performance. The ability to reconfigure I/Os as inputs or outputs offers great flexibility in board layout.
4. Power Supply Decoupling: Like all high-speed CMOS devices, proper decoupling with 0.1 μF capacitors placed close to the VCC and GND pins is essential to suppress noise and ensure stable operation.
5. Programming and Security: The device features an electronic security fuse that, once programmed, prevents the programmed pattern from being copied or read back, protecting intellectual property.
The GAL22V10D-10LJN excels in applications such as address decoding, bus interfacing, state machine control, glue logic consolidation, and as a programmable replacement for numerous standard logic ICs.
The Lattice GAL22V10D-10LJN stands as a testament to simple, effective, and power-efficient programmable logic. Its macrocell-based architecture provides an ideal blend of flexibility and performance for a host of glue logic and control applications, bridging the gap between discrete logic and more complex programmable devices.
Keywords:
1. Programmable Logic Device (PLD)
2. Output Logic Macrocell (OLMC)
3. Reprogrammable
4. Combinatorial and Sequential Logic
5. Low Power Dissipation
