Intel N28F001BX-B120: A Comprehensive Technical Overview of the 1-Megabit Boot Block Flash Memory Chip
The Intel N28F001BX-B120 stands as a significant component in the historical development of non-volatile memory solutions. This 1-megabit (1 Mbit) CMOS flash memory chip, organized as 128K x 8, was engineered for a primary critical application: storing system firmware or BIOS that a microprocessor could directly execute upon power-up. Its innovative Boot Block architecture was its most defining feature, setting a standard for secure and reliable firmware storage.
Fabricated using Intel's advanced CMOS technology, the device offered a superior alternative to the older EPROM or EEPROM solutions. It provided in-system reprogrammability without the need for removal from the circuit board, significantly easing the process of field upgrades and firmware maintenance. The chip operated from a single +5V power supply for both program and erase operations, simplifying system power design.
The core of the N28F001BX-B120's design is its asymmetrically segmented memory array. Unlike a uniform flash array, it was divided into multiple blocks:
One 16-Kbyte Boot Block: This block, typically located at the highest or lowest memory address, was the cornerstone of its design. It could be locked with a hardware pin (RP/PWD) to protect the critical boot code from accidental or malicious corruption during the rest of the array's update process.
Two 8-Kbyte Parameter Blocks: These smaller blocks were intended for storing frequently updated parameters or configuration data.
One 96-Kbyte Main Block: This large main array was used for storing the bulk of the application code or data.
This flexible sector architecture allowed for individual block erasure, meaning a single parameter block could be rewritten without affecting the integrity of the boot code or the main firmware section. The device featured a standard JEDEC-approved pinout, ensuring compatibility with other x8 memories and simplifying socket design.
Command execution followed the standard write state machine protocol common to Intel flash memories of that era. By writing specific command sequences into the command register, the microprocessor could place the device into various modes like read, program, erase, or erase suspend. This interface abstracted the complexities of the internal programming algorithms, such as Intelligent Programming and Intelligent Erase, which used internal timers and verify circuits to ensure each cell was programmed or erased to the correct threshold.
The part number suffix B120 indicates a 120ns maximum access time, making it suitable for use with a wide range of microprocessors without requiring wait states. The chip also offered low power consumption, with a typical active current of 30 mA and a standby current of just 100 µA, enhancing its suitability for power-sensitive applications.
ICGOOODFIND: The Intel N28F001BX-B120 was a pioneering force in the flash memory market, cementing the boot block concept as an industry best practice for firmware storage. Its combination of hardware-based code protection, flexible in-system reprogrammability, and robust performance made it an indispensable component in countless computing and embedded systems throughout the 1990s, ensuring system stability and enabling secure field updates.
Keywords: Boot Block Flash Memory, In-System Reprogrammability, Hardware Code Protection, Asymmetric Sector Architecture, Non-Volatile Memory.
