Microchip Technology 24AA256UID-I/ST

Overview

24AA256UID-I/ST from Microchip Technology Inc. is a 32K × 8 (256 Kbit) I²C-compatible 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, and 64-byte page write buffer. It operates across -40°C to +85°C and supports up to eight devices on one bus via A0–A2 address pins.

For engineers reviewing the 24AA256UID-I/ST datasheet, 24AA256UID-I/ST pinout, 24AA256UID-I/ST application, or 24AA256UID-I/ST equivalent, this device delivers deterministic UID-based device identification, robust noise-immune I²C timing (Schmitt-trigger inputs, slope-controlled outputs), and permanent write-protection of identity data in the upper 1/8th of memory - critical for secure boot, asset tracking, and network node provisioning.

Technical Context

The 24AA256UID-I/ST implements a standard two-wire I²C slave interface with fixed 4-bit control code '1010', three programmable chip-select bits (A0–A2), and R/W bit-driven read/write mode selection. Its internal address pointer auto-increments during sequential reads and wraps at 0x7FFF.

It uses on-chip charge pump for EEPROM programming, enforces strict page-boundary alignment for writes (64-byte pages starting at multiples of 0x0040), and permanently locks identity data (EUI-48 at 0x7F7A–0x7F7F, EUI-64 at 0x7FB8–0x7FBF, 32-bit UID at 0x7FFC–0x7FFF) in the write-protected 0x7000–0x7FFF region.

Key Specifications

Pinout & Package

8-pin SOIC package (3.9mm × 4.9mm, 1.27mm pitch); RoHS compliant; marked "4A256IDI" with temperature grade "I" and date code.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar serial EEPROM with UID applications.

Compared with 24LC256UID-I/SN, the 24AA256UID-I/ST enables true single-supply operation down to 1.7V and offers superior data retention. Against AT24MAC402-MAHM-T, it provides full EUI-64 and scalable UID lengths - essential for IPv6-ready and cryptographic key binding use cases.

Availability

24AA256UID-I/ST is available at Aetrix Electronics and suitable for secure boot, industrial asset tagging, network equipment provisioning, and medical device calibration traceability requiring stable component supply and guaranteed UID uniqueness.

Supply support for 24AA256UID-I/ST 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 U.S.-based semiconductor manufacturer specializing in microcontrollers, analog devices, and memory solutions for industrial, automotive, and communications markets.

The 24AA256UID-I/ST belongs to Microchip's UID-family of serial EEPROMs, designed specifically to provide factory-programmed, globally unique identifiers for secure device authentication, network node addressing, and regulatory-compliant traceability in mission-critical systems.

FAQ

What is the exact memory organization of the 24AA256UID-I/ST, and where are the UID/EUI values stored?

The 24AA256UID-I/ST contains 32K × 8 bits (256 Kbit) organized as 32,768 bytes. The upper 1/8th (0x7000–0x7FFF) is permanently write-protected. Within that region: EUI-48™ is at 0x7F7A–0x7F7F, EUI-64™ at 0x7FB8–0x7FBF, and the 32-bit serial number at 0x7FFC–0x7FFF. The 24AA256UID-I/ST also stores manufacturer code (0x29) at 0x7FFA and device identifier (0x48) at 0x7FFB.

Does the 24AA256UID-I/ST support I²C clock stretching or multi-master arbitration?

No, the 24AA256UID-I/ST does not support clock stretching or multi-master arbitration. It operates strictly as an I²C slave with fixed timing parameters and no hold capability on SCL. Multi-master bus contention must be managed externally by the master controller. The 24AA256UID-I/ST relies on acknowledge polling (via repeated Start + control byte) to detect ongoing internal write cycles.

Can the 24AA256UID-I/ST be used in a 1.8V system, and what are the I²C timing implications?

Yes, the 24AA256UID-I/ST supports 1.7V–5.5V operation, making it fully compatible with 1.8V systems. At VCC < 2.5V, maximum I²C clock frequency is limited to 100 kHz, with adjusted timing: THIGH ≥ 4000 ns, TLOW ≥ 4700 ns, and TR/TF up to 1000 ns. These relaxed timings ensure reliable communication under low-voltage conditions.

How is write protection enforced on the 24AA256UID-I/ST, and can it be disabled?

Write protection on the 24AA256UID-I/ST is hardware-permanent for the upper 1/8th of memory (0x7000–0x7FFF). This region - containing EUI-48, EUI-64, and the 32-bit serial number - cannot be unlocked or modified after factory programming. The 24AA256UID-I/ST does not implement software write-protect bits or WP pin functionality; protection is intrinsic and irreversible.

What is the maximum number of 24AA256UID-I/ST devices that can share one I²C bus, and how is addressing managed?

Up to eight 24AA256UID-I/ST devices can share a single I²C bus using the A0, A1, and A2 address pins. These three pins form the LSBs of the 7-bit slave address (base '1010' + A2A1A0), yielding eight unique addresses (0xA0–0xA7 for write, 0xA1–0xA8 for read). Each 24AA256UID-I/ST must have a distinct A2:A1:A0 combination to avoid bus collisions.