Lattice GAL22V10D-10LP: Architecture, Features, and Application Design Considerations
The Lattice GAL22V10D-10LP stands as a classic and enduring architecture within the realm of programmable logic devices (PLDs). As a member of the Generic Array Logic (GAL) family, it provides a robust, electrically erasable, and cost-effective solution for implementing a wide variety of combinatorial and sequential logic functions. Its architecture is centered around a programmable AND array feeding into a fixed OR array, a structure known as PAL® (Programmable Array Logic). The key innovation of the GAL over its PAL predecessors is the inclusion of Output Logic Macro Cells (OLMCs), which provide tremendous design flexibility.
Architecture and Core Features
The "22V10" nomenclature is descriptive of its core architecture: it features 22 inputs and 10 output logic macrocells. Each macrocell can be configured by the designer to operate in various modes, making the device incredibly versatile.
The internal architecture consists of:
Programmable AND Array: This forms the product terms for the logic functions. The array is electrically erasable (E²CMOS technology), allowing for both prototyping and design changes with ease.
Fixed OR Array: Each OR gate aggregates a specific number of product terms from the AND array and feeds them into its corresponding OLMC.
Output Logic Macro Cells (OLMCs): This is the heart of the device's flexibility. Each OLMC contains a register (D-type flip-flop) and multiplexers that allow each pin to be configured as:
A dedicated input
A combinatorial output (active high or active low)
A registered output (active high or active low)
A bidirectional I/O pin
The macrocell also features individual programmable output enable terms, allowing for sophisticated bus interface control.
The "-10LP" suffix specifically denotes a 10 ns maximum propagation delay (tPD) and "Low Power" operation. This combination of high speed and reduced power consumption makes it suitable for performance-oriented and power-sensitive applications.
Key Design Considerations
When designing with the GAL22V10D-10LP, several critical factors must be considered to ensure a successful implementation:
1. Product Term Limitations: Each output has a specific number of product terms allocated to it (ranging from 8 to 16 per output in the 22V10). Complex logic functions requiring many AND terms may need to be optimized or split across multiple outputs. Efficient logic minimization is paramount.
2. Clock and Reset Resources: The device has a dedicated clock pin (CLK) and a dedicated output enable/async reset pin (OE/AR). These signals are common to all registered macrocells. Designs must be synchronous to a single clock edge, and asynchronous reset must be globally applied.
3. Power-On Reset (POR) Behavior: The E²CMOS technology provides a predictable power-on state. All registers are reset to a low state upon power-up, which is a crucial feature for ensuring deterministic startup behavior in state machines.
4. SSO (Simultaneous Switching Output) Noise: When a large number of outputs switch states simultaneously, ground bounce and VCC noise can occur. Proper decoupling (a 0.1μF capacitor close to the VCC and GND pins) and careful pin assignment to minimize the number of outputs switching at the same time are essential practices.
5. Toolchain and Fitting: While modern EDA tools can handle these devices, the JEDEC file generated after fitting must be carefully reviewed. It is vital to confirm that the compiler has correctly implemented the desired logic within the architectural constraints of the device.
Application Spaces
The GAL22V10D-10LP finds its strength in "glue logic" applications, where it integrates multiple discrete TTL logic packages into a single, customizable chip. Common applications include:
Address decoding and chip select generation in microprocessor systems.
Interface logic between components with different protocols or timing.
State machine implementation for simple control sequences.
Bus interfacing and signal conditioning.
Conversion of parallel data to serial formats and vice-versa.
The Lattice GAL22V10D-10LP remains a quintessential PLD, offering a perfect blend of design flexibility, predictable timing, and low power consumption. Its well-defined architecture of a programmable AND array feeding into configurable OLMCs makes it an ideal choice for consolidating glue logic, implementing fast state machines, and simplifying board design. While newer CPLDs and FPGAs offer greater capacity, the GAL22V10D-10LP continues to be a reliable, cost-effective, and low-risk solution for a vast array of digital logic tasks, cementing its status as a workhorse of programmable logic.
Keywords:
Programmable Logic Device (PLD)
Output Logic Macro Cell (OLMC)
Propagation Delay (tPD)
Glue Logic
JEDEC File
