Intel RC28F256J3F95: A Deep Dive into the 256Kb ETOX Flash Memory Chip

In the landscape of semiconductor memory, Intel's introduction of the ETOX (EPROM Tunnel Oxide) technology was a pivotal moment, paving the way for modern flash memory. The Intel RC28F256J3F95 stands as a classic embodiment of this innovation, a 256-kilobit (32KB) CMOS-compatible flash memory chip that helped define an era of non-volatile storage. This deep dive explores its architecture, functionality, and enduring significance.

Constructed with Intel's advanced 1.0-micron ETOX IV process technology, this chip offered a remarkable blend of performance and reliability for its time. Its core architecture is organized as 32,768 words by 8 bits, providing a straightforward byte-wide interface that simplified integration into microprocessor-based systems, which were predominantly 8-bit and 16-bit.

A key feature of the RC28F256J3F95 was its 12.0-volt VPP programming voltage. Unlike modern single-power-supply chips, this device required a separate, higher voltage for the program and erase operations, a common characteristic of early flash memories. The chip supported a fast programming algorithm, allowing entire memory contents to be written in a matter of seconds. More importantly, it featured a 100,000 program/erase cycle endurance per sector, a specification that guaranteed robust performance over the product's lifetime.

The device offered superior data protection. It integrated both a programming lockout mechanism during power transitions and a command-driven software data protection feature. This prevented accidental corruption of the stored firmware, which is critical for embedded systems where reliability is paramount. Furthermore, its access times were sufficiently fast to allow execution directly from the chip (XIP - eXecute In Place), eliminating the need for shadow RAM in many applications.

Housed in a 32-pin PLCC (Plastic Leaded Chip Carrier) or TSOP package, the RC28F256J3F95 found its home in a vast array of late-1980s and 1990s technology. It was the silent workhorse storing BIOS in personal computers, firmware in networking equipment, and critical code in industrial control systems. Its durability and proven technology made it a preferred choice for developers who could not afford the risk of data loss.

ICGOOODFIND: The Intel RC28F256J3F95 is more than a obsolete component; it is a foundational artifact in the history of computing. It exemplifies the transition from EPROM to easily rewritable flash memory, showcasing the ETOX technology that became the industry standard. Its design principles of reliability, sector protection, and compatibility directly influenced the development of the higher-density flash memories that power today's world. For engineers and historians alike, it remains a benchmark of robust and effective memory design.

Keywords: ETOX Flash Memory, Non-Volatile Storage, VPP Programming, Program/Erase Endurance, CMOS-Compatible.