Intel PC28F256P33B85: A Comprehensive Technical Overview of the 256-Megabit Parallel NOR Flash Memory

The Intel PC28F256P33B85 stands as a significant component within the landscape of non-volatile memory solutions, representing a high-density, parallel NOR Flash memory device designed for demanding embedded applications. This 256-megabit (32-megabyte) memory chip combines high-performance read operations with reliable storage capabilities, making it a cornerstone in systems where execution-in-place (XIP) functionality is critical, such as networking equipment, telecommunications infrastructure, industrial control systems, and avionics.

Architecture and Core Features

Organized as 32,768K words of 8 bits each (32M x 8), the device features a symmetric memory array architecture that simplifies design and addressing. Its primary interface is a parallel, multiplexed address and data bus, which allows for rapid data transfer and direct connection to industry-standard microprocessors and microcontrollers.

A key attribute of this memory is its impressive speed. The "P33" in its part number signifies a fast 90ns maximum random access time (for the -85 speed grade), enabling zero-wait-state operation with high-performance processors running at clock speeds up to approximately 66 MHz. This low latency is paramount for fetching boot code and application instructions directly from the flash, eliminating the need to shadow code into faster RAM and thus reducing system cost and complexity.

Advanced Functionality and Reliability

The PC28F256P33B85 is built on Intel's advanced 0.13μm MirrorBit® NOR Flash technology. This process technology is renowned for its inherent reliability and high manufacturing yields. The device operates on a single 3.0V - 3.6V power supply (VCC) for all read, program, and erase operations, contributing to lower overall system power consumption.

It incorporates a sophisticated Command Set Architecture, which is compatible with the Common Flash Memory Interface (CFI), allowing host software to automatically query the flash device to identify its manufacturer, size, and electrical parameters. This simplifies system design and firmware porting across different flash densities.

For code protection and security, the chip offers a robust hardware and software lock mechanism. This includes block locking and a dedicated write-protect pin (`WP`) to prevent accidental or malicious modification of critical boot sectors. Furthermore, it provides 512-byte of One-Time Programmable (OTP) memory for storing secure, immutable data like encryption keys or unique device identifiers.

Programming and Erase Operations

Unlike its simpler read-only counterparts, this NOR flash supports in-system reprogramming. It utilizes a high-speed programming algorithm that can program a full 32-byte write buffer in approximately 25μs. The erase function is organized into 128 KB uniform blocks, providing flexible memory management. Each block can endure a minimum of 100,000 program/erase cycles, ensuring long-term durability for firmware updates throughout the product's lifecycle. Data retention is specified at an exceptional 20 years, guaranteeing data integrity over decades.

Conclusion and Applications

The Intel PC28F256P32B85 is a workhorse of reliability and performance in the parallel NOR flash segment. Its combination of fast random access, XIP capability, advanced sector protection, and high endurance makes it an ideal choice for storing and executing boot code, operating systems, and application firmware in mission-critical systems that cannot afford the latency of serial flash or the volatility of RAM.

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Keywords:

1. Parallel NOR Flash

2. Execute-in-Place (XIP)

3. 256-Megabit

4. 3.0V Supply

5. Block Locking