Lattice GAL18V10B-15LP: Architecture, Key Features, and Target Applications
The Lattice GAL18V10B-15LP 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 powerful, erasable, and pin-compatible successor to older PAL devices, revolutionizing digital logic design in its era. This article delves into its internal architecture, highlights its key features, and explores its primary applications.
Architecture: A Look Inside
The GAL18V10B-15LP is based on a well-established Programmable Logic Device (PLD) architecture. Its structure is fundamentally composed of two main sections: a programmable AND array and a fixed OR array feeding into output logic macrocells (OLMCs).
The "18V10" designation reveals its core configuration: it has 10 dedicated output logic macrocells (OLMCs), each of which can be configured for various output modes (combinatorial, registered, or bidirectional I/O). The device features a maximum of 12 dedicated inputs and 10 I/O pins, which can be configured as inputs if the output macrocell is not used, providing significant flexibility. The programmable AND array generates product terms from these inputs, which are then summed by the fixed OR array to create the desired logic functions. A key architectural advantage was its electrically erasable (E²) CMOS technology, which allowed designers to reprogram the device thousands of times, a significant improvement over one-time programmable (OTP) parts.
Key Features
The GAL18V10B-15LP integrated several features that made it a designer favorite for countless projects.
High Performance: The "-15" in its part number signifies a maximum pin-to-pin propagation delay of 15 nanoseconds, making it suitable for a wide range of high-speed logic applications.
Low Power Consumption: Fabricated in CMOS technology, it offered very low power dissipation, a critical feature for power-sensitive designs. The "LP" suffix often denotes "Low Power."
100% Testability: The architecture supported full functional testability, ensuring high reliability and manufacturing yield.
Erasability and Reusability: The use of E²CMOS technology meant designs could be prototyped, tested, and modified rapidly without discarding hardware, drastically reducing development time and cost.
Pin Compatibility: It was designed to be a drop-in replacement for a wide range of older 20-pin PAL devices (like the PAL16L8 and PAL16R8), allowing for easy design upgrades and migration to a reprogrammable platform.
Target Applications
While newer and more complex CPLDs and FPGAs have taken over most modern design tasks, the GAL18V10B-15LP was the go-to solution for a vast array of "glue logic" and system interface functions. Its primary target applications included:
Address Decoding: Generating chip select signals for microprocessors and microcontrollers (e.g., 8051, 68HC11, Z80).
State Machine Control: Implementing simple but critical finite state machines (FSMs) for controlling system processes.
Bus Interface Logic: Acting as an interface between components with slightly different signaling protocols or timing requirements.
I/O Expansion and Data Gating: Managing data flow and expanding the I/O capabilities of a central processing unit.
Code Conversion and Signal Conditioning: Converting between binary codes (e.g., BCD to binary) and conditioning digital signals.
The Lattice GAL18V10B-15LP is a quintessential example of an innovative PLD that empowered a generation of engineers. Its blend of high speed, low power, reprogrammability, and pin-compatibility solidified its role as a fundamental building block in digital systems, effectively bridging the gap between discrete logic and more complex programmable devices.
Keywords: Programmable Logic Device (PLD), Output Logic Macrocell (OLMC), Electrically Erasable (E²CMOS), Glue Logic, Address Decoding
