Lattice GAL22V10D-15LPNI: Architecture, Key Features, and Target Applications

The Lattice GAL22V10D-15LPNI stands as a classic 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 electrically reprogrammable alternative to one-time programmable PAL devices, revolutionizing digital design prototyping and low-to-medium volume production.

Architecture: A Look Inside

The architecture of the GAL22V10D is a masterpiece of structured programmability. Its designation, "22V10," succinctly describes its core structure:

22 Inputs: The device features 12 dedicated input pins and 10 input/output (I/O) pins that can also be configured as inputs, providing a flexible interface to the external circuit.

10 Outputs: The 10 I/O pins are primarily used as outputs, each driven by a sophisticated Output Logic Macrocell (OLMC).

Programmable AND Array / Fixed OR Array: This is the fundamental architecture. A user-programmable AND array generates product terms from the input signals. These product terms are then fed into a fixed OR array, which sums them together to create sum-of-product logic functions for each output.

Output Logic Macrocell (OLMC): This is the key to the device's flexibility. Each of the ten outputs is controlled by its own OLMC, which can be configured through programming to operate in various modes: combinatorial or registered (clocked), with output polarity control (active-high or active-low). This allows each pin to be defined as a dedicated input, a combinatorial output, or a registered output, making the chip incredibly versatile.

Key Features and Specifications

The "D-15LPNI" suffix provides specific details about the device's performance and packaging:

High Performance: The -15 denotes a maximum propagation delay (`tPD`) of 15 nanoseconds, enabling operation at high clock speeds for its era.

Low Power: The L in the part number signifies Low Power technology, typically half the power consumption of standard GAL devices, making it suitable for power-sensitive applications.

Electrically Erasable: The GAL22V10D utilizes EEPROM (E2CMOS) technology. This allows the device to be reprogrammed and erased electrically, thousands of times, drastically accelerating design iteration and debugging compared to UV-erasable or one-time programmable parts.

100% Testability: The architecture supports JTAG or similar test functionality, ensuring high fault coverage during manufacturing.

Package: The PN indicates a 28-pin Plastic Dual-In-Line Package (PDIP), a through-hole package common for prototyping.

Target Applications

While largely superseded by more complex CPLDs and FPGAs for new designs, the GAL22V10D-15LPNI was and still is targeted at a wide range of applications:

Address Decoding: Perfect for generating chip select (`/CS`) and read/write signals in microprocessor and microcontroller-based systems.

State Machine Control: Its registered outputs are ideal for implementing medium-complexity finite state machines (FSMs) for control logic.

Glue Logic Integration: Its primary historical role was to replace multiple simple TTL logic chips (e.g., 74-series) with a single, programmable device, reducing board space, component count, and improving reliability.

Bus Interfacing: Used for protocol conversion and signal conditioning between different digital subsystems.

Educational Tool: It remains an excellent tool for teaching digital logic design fundamentals, from basic Boolean equations to state machines.

ICGOODFIND Summary

The Lattice GAL22V10D-15LPNI is a foundational pillar of programmable logic. Its elegant blend of a programmable AND array, fixed OR array, and highly configurable output macrocells provided engineers with an unprecedented level of design flexibility and integration for its time. While its raw logic capacity is modest by today's standards, its architectural principles live on, and it remains a reliable, low-power solution for replacing fixed logic and implementing control functions in legacy systems and new, simple designs.

Keywords:

Programmable Logic Device (PLD)

Generic Array Logic (GAL)

Output Logic Macrocell (OLMC)

Glue Logic

EEPROM