Microchip Technology 24AA256UID-I/P

Overview

24AA256UID-I/P from Microchip Technology Inc. is a 256 Kbit I²C serial EEPROM with factory-programmed EUI-48™ and EUI-64™ node addresses, a unique 32-bit serial number, 1.7V–5.5V single-supply operation, 64-byte page write buffer, and industrial temperature range (−40°C to +85°C). It serves as a secure identity and configuration storage device in networked embedded systems requiring guaranteed uniqueness and tamper-resistant identification.

For engineers reviewing the 24AA256UID-I/P datasheet, 24AA256UID-I/P pinout, 24AA256UID-I/P application, or 24AA256UID-I/P equivalent, this device delivers deterministic node addressing, permanent UID storage in write-protected memory, low-power I²C interface compatibility up to 400 kHz, Schmitt-trigger noise immunity, and cascading support for up to eight devices on one bus.

Technical Context

The 24AA256UID-I/P implements a standard two-wire I²C slave interface with fixed 7-bit address prefix '1010', user-configurable A0–A2 chip select bits enabling up to eight devices per bus, and automatic address pointer incrementing during sequential reads. Its internal architecture includes a 64-byte page latch, dedicated HV generator for EEPROM programming, and permanently write-protected upper 1/8th memory region (0x7000–0x7FFF) housing identifiers.

It supports three read modes-current address, random, and sequential-and two write modes-byte and page-with self-timed erase/write cycles (≤5 ms), acknowledge polling for cycle completion detection, and built-in slope control on SDA/SCL to suppress ground bounce. All I/O pins feature Schmitt-trigger inputs and ESD protection >4 kV.

Key Specifications

Pinout & Package

24AA256UID-I/P is packaged in an 8-lead PDIP (plastic dual in-line package) with 300-mil body width, RoHS-compliant matte tin lead finish, and standard through-hole mounting. Pin 1 is marked with a notch or dot; pin numbering follows counterclockwise convention from top-left when viewed with marking side up.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar serial EEPROM with factory-programmed identity applications.

Compared with 24AA256-I/P, the 24AA256UID-I/P adds immutable identity storage without sacrificing memory capacity or interface compatibility; compared with AT24MAC402-MAHM-T, it offers larger user-accessible memory and dual EUI-48/EUI-64 support essential for IPv6 and heterogeneous network stacks.

Availability

24AA256UID-I/P is available at Aetrix Electronics and suitable for industrial automation, medical diagnostics, smart metering, and networked sensor applications requiring stable component supply, guaranteed device uniqueness, and long-term data integrity.

Supply support for 24AA256UID-I/P includes scheduled delivery planning, volume procurement assistance, BOM continuity management, traceable sourcing, and lifecycle availability coordination for OEM customers, industrial embedded developers, connected-device designers, and electronics production programs.

Manufacturer

Microchip Technology Inc. is a leading provider of microcontroller, analog, FPGA, and memory solutions, headquartered in Chandler, Arizona, with global design, manufacturing, and sales operations.

The 24AA256UID-I/P belongs to Microchip's UID-family of serial EEPROMs, designed specifically to simplify device identity management in IoT, industrial, and medical systems by embedding globally unique identifiers directly into nonvolatile memory at wafer-level test.

FAQ

What is the exact memory organization of the 24AA256UID-I/P, and how much user-accessible space is available?

The 24AA256UID-I/P contains 256 Kbit (32,768 × 8) total EEPROM memory. The upper 1/8th (0x7000–0x7FFF = 4,096 bytes) is permanently write-protected and holds factory-programmed identifiers: EUI-48™ (0x7F7A–0x7F7F), EUI-64™ (0x7FB8–0x7FBF), and 32-bit serial number (0x7FFC–0x7FFF). This leaves 229,376 bits (28,672 bytes) from 0x0000–0x6FFF fully writable for application use. The 24AA256UID-I/P datasheet confirms this partitioning in Figure 9-1 and Section 9.0.

Does the 24AA256UID-I/P support both 100 kHz and 400 kHz I²C clock speeds across its full voltage range?

No-the 24AA256UID-I/P supports 400 kHz I²C operation only when VCC ≥ 2.5V; below 2.5V, maximum clock frequency is limited to 100 kHz. This is explicitly specified in Table 1-2 (AC Characteristics) and the Device Selection Table. The 24AA256UID-I/P maintains full functionality-including UID access and page writes-at both speeds, but timing parameters (e.g., THIGH, TLOW, TR/TF) differ per voltage band per DS20005215D-page 3.

How is the factory-programmed 32-bit serial number accessed, and what guarantees its uniqueness?

The 32-bit serial number resides at fixed memory addresses 0x7FFC–0x7FFF and is readable via standard I²C random or sequential read commands. Its uniqueness is guaranteed across all Microchip UID-family EEPROMs (including 24AA02UID, 24AA025UID, etc.) because it is programmed during wafer-level testing using a centralized, monotonically increasing counter. The 24AA256UID-I/P datasheet states this in Section 9.1 and the Features list on page 1.

Can the 24AA256UID-I/P be used in a system with multiple I²C masters, and what arbitration behavior does it exhibit?

The 24AA256UID-I/P operates exclusively as an I²C slave device and does not implement multi-master arbitration logic. It responds only to START conditions and address matches initiated by an external master. In systems with multiple masters, bus arbitration must be handled entirely by the masters per I²C specification; the 24AA256UID-I/P remains transparent during arbitration and will respond only after a winning master asserts control. This behavior is defined in Section 3.0 and Figure 4-1 of the 24AA256UID-I/P datasheet.

What is the purpose of the NC (No Connect) pin on the 24AA256UID-I/P PDIP package, and can it be tied to ground or VCC?

The NC pin (Pin 7 in 8-lead PDIP, SOIC, and TSSOP packages) is internally unconnected and must remain floating-neither grounded nor tied to VCC. Connecting it may cause unpredictable leakage paths or violate absolute maximum ratings. The 24AA256UID-I/P Pin Function Table (Table 2-1, DS20005215D-page 5) explicitly defines Pin 7 as "Not Connected", and the Absolute Maximum Ratings table prohibits any voltage outside −0.6V to VCC+1.0V on this terminal. Leaving it unconnected ensures reliable operation per 24AA256UID-I/P specifications.