Lattice GAL22V10C-7LJ: Architecture, Key Features, and Application Design Considerations
The Lattice GAL22V10C-7LJ stands as a classic and highly influential device in the realm of programmable logic. As a member of the Generic Array Logic (GAL) family, it provided a pioneering, erasable alternative to one-time programmable PAL devices, significantly accelerating digital design prototyping and development. This article delves into the architecture, core features, and critical design considerations for this enduring integrated circuit.
Architecture: A Look Inside
The GAL22V10C-7LJ is based on a well-established Programmable AND-Fixed OR architecture, which is the fundamental structure of most Simple Programmable Logic Devices (SPLDs). Its internal structure can be broken down into several key components:
Input/Output Logic Macrocell (OLMC): The heart of the GAL's flexibility. The device features 10 output logic macrocells, each of which can be individually configured. Each macrocell contains a programmable array of AND gates feeding into an OR gate, a flip-flop (D-type), and multiplexers that control signal routing.
Programmable AND Array: This is the programmable segment of the architecture. It consists of a grid of fusible links that define the logical connections between the input terms and the product terms fed into the OR gate. The "22" in its name refers to the maximum number of input terms available to this array.
Fixed OR Array: Each macrocell has a fixed number of product terms allocated to its OR gate, which then feeds into the macrocell's logic.
Clock and Output Enable: The device features a dedicated clock pin (CLK) for all registered outputs and a dedicated output enable (OE) pin, providing centralized control for the output buffers.
Key Features and Specifications
The "C" in its part number signifies that it is built on CMOS technology, offering lower power consumption than its bipolar predecessors. The "-7LJ" suffix denotes its speed grade and package type (PLCC).
High Performance: The -7 speed grade indicates a maximum propagation delay (Tpd) of 7.5 ns, making it suitable for high-speed logic integration.
Re-programmability: Unlike one-time programmable (OTP) PALs, the GAL22V10C uses an EEPROM cell technology, allowing it to be erased and reprogrammed上百次, facilitating design iteration and debugging.
CMOS Low Power: The CMOS design offers significantly lower standby and active power consumption.
10 Output Logic Macrocells: Each of the 10 I/O pins can be configured as an input, a registered output, or a combinatorial output, providing immense flexibility for state machine and logic implementation.
28-pin PLCC Package: The J-lead PLCC package was a industry standard, offering a compact footprint and reliable soldering.
Application Design Considerations
When designing with the GAL22V10C-7LJ, several factors must be carefully considered to ensure a successful implementation:
1. Product Term Limitations: While powerful, the GAL has a finite number of product terms per output. Complex logic functions can easily exhaust these resources. Designers must minimize logic equations using Boolean algebra or synthesis tools to fit within these constraints.
2. Clock and Reset Management: The single, global clock and asynchronous reset signals are distributed to all macrocells. Designs must be synchronous to this clock for reliable operation. Care must be taken with gated clocks or derived clock enables to avoid potential skew and glitches.
3. Pin-Locking Strategy: For designs that may require future changes, it is crucial to plan a pin-locking strategy early. This involves assigning critical inputs (clock, reset, enables) and outputs to specific pins and avoiding changes to them in future revisions to maintain PCB compatibility.
4. Power-On Reset and State: The power-on state of the internal registers can be unpredictable. For critical applications, an external reset circuit should be implemented to force the device into a known state upon power-up.
5. Software Toolchain: While modern tools may have limited support, period-specific software like CUPL or Abel was used to compile logic equations into the JEDEC fuse map file used to program the device. Understanding the syntax and capabilities of these tools is essential.
The Lattice GAL22V10C-7LJ is more than just a chip; it is a milestone in the evolution of digital logic design. It democratized programmability, offering a perfect blend of speed, flexibility, and re-programmability that made it an indispensable tool for a generation of engineers for implementing glue logic, state machines, and address decoders. While largely supplanted by more dense CPLDs and FPGAs today, its architectural principles remain foundational.
Keywords:
Programmable Logic Device (PLD)
Output Logic Macrocell (OLMC)
CMOS Technology
Re-programmable
Propagation Delay (Tpd)
