Lattice Semiconductor ISPLSI2064-80LT: A Comprehensive Technical Overview of the High-Density CPLD

In the realm of digital logic design, Complex Programmable Logic Devices (CPLDs) serve as a critical bridge between simple PLDs and high-capacity FPGAs. The Lattice Semiconductor ISPLSI2064-80LT stands as a prominent representative of high-density CPLD technology from its era, offering a robust combination of capacity, performance, and in-system programmability. This article provides a detailed technical examination of this specific device.

The ISPLSI2064-80LT is a member of Lattice's renowned ispLSI 2000VE family. The nomenclature itself is descriptive: "ISPLSI" denotes the in-system programmable logic family, "2064" indicates it contains 64 macrocells, and the "-80LT" suffix specifies both speed grade (80ns pin-to-pin delay) and package (LT representing a Thin Quad Flat Pack, TQFP).

At the core of its architecture is a super-wide input gating array that efficiently feeds a programmable logic structure. The device is organized into two Generic Logic Blocks (GLBs), each containing 32 macrocells. This macrocell count was considered high-density at the time, enabling the integration of numerous discrete logic components into a single, compact chip. Each macrocell consists of a programmable AND-OR array and a configurable register that can be set for D, T, JK, or SR flip-flop operation, or bypassed for combinatorial logic. The device features 108 user-programmable I/O pins, providing extensive connectivity to the outside world. These I/Os are organized into bi-directional I/O cells, which can be configured for various logic standards and feature slew rate control.

A defining characteristic of this device is its In-System Programmability (ISP). Utilizing a simple 5-wire interface (SDI, SDO, MODE, SCLK, and ispEN), the CPLD can be reprogrammed while soldered onto its final printed circuit board (PCB). This capability drastically simplifies the design iteration process, reduces time-to-market, and allows for field upgrades, which was a significant advantage over older, one-time-programmable (OTP) devices.

The timing specification highlighted by the "-80" grade is crucial. The 80ns maximum pin-to-pin delay signifies a guaranteed maximum propagation delay for any signal path through the device, allowing designers to confidently meet critical timing requirements in their systems. The device operates on a 5.0-volt core voltage, which was standard for the period.

The compact TQFP package makes it suitable for space-constrained applications. Typical applications for the ISPLSI2064-80LT included complex state machine control, high-speed address decoding, glue logic integration in computer systems, bus interfacing, and protocol bridging. It served to consolidate many smaller-scale integrated circuits, thereby improving system reliability, reducing board space, and lowering overall power consumption.

ICGOOODFIND: The Lattice Semiconductor ISPLSI2064-80LT exemplifies the peak of 5V high-density CPLD technology. Its key strengths lie in its significant logic integration capacity for its class, true in-system programmability, and predictable high-performance timing. While newer families have surpassed it in density, speed, and moved to lower voltages, this device remains a classic example of a workhorse CPLD that empowered a generation of digital designers to create more integrated and sophisticated electronic systems.

Keywords: High-Density CPLD, In-System Programmability (ISP), 64 Macrocells, 5.0-Volt Operation, Generic Logic Block (GLB)