Microchip Technology AT28HC256-12SU-T

Overview

AT28HC256-12SU-T from Microchip Technology is a 256-Kbit (32,768 × 8) parallel EEPROM with 120 ns read access time, single 5V ±10% supply operation, JEDEC-approved byte-wide pinout, and industrial temperature range (–40°C to +85°C). It supports automatic 1–64-byte page writes with internal latching and data polling for write completion detection, deployed in embedded control firmware storage and configuration memory applications.

For engineers reviewing the AT28HC256-12SU-T datasheet, AT28HC256-12SU-T pinout, AT28HC256-12SU-T application, or AT28HC256-12SU-T equivalent, key selection criteria include its 120 ns AC read timing, hardware/software data protection, 10,000/100,000 write endurance, 10-year data retention, and compatibility with legacy SRAM-style bus interfaces.

Technical Context

The AT28HC256-12SU-T implements a static RAM-compatible parallel interface with dual-line chip enable (CE) and output enable (OE) control to prevent bus contention. Its internal 64-byte page register enables burst loading of up to 64 bytes per write cycle, with address latching on the falling edge of CE or WE and data latching on the subsequent rising edge.

Write completion is verified via DATA Polling (I/O7 complement toggle) or Toggle Bit (I/O6 toggling), both usable at any point during the internal programming period. Hardware protection includes VCC sense (<3.8 V inhibits write), 5 ms power-on delay, noise filtering (<15 ns pulses ignored), and write-inhibit logic (OE high, CE high, or WE high blocks writes).

Key Specifications

Pinout & Package

AT28HC256-12SU-T is packaged in a 28-lead SOIC (Small Outline Integrated Circuit) with JEDEC-standard byte-wide pinout. Pin 1 is index-marked; pins are arranged for direct replacement into existing 28-pin parallel memory footprints.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar parallel EEPROM applications.

Compared with AT28HC256-12SU-T, AT28C256-12PU offers identical electrical behavior in a through-hole package but lacks RoHS compliance, while M95256-DW trades parallel speed and simplicity for serial interface compactness-requiring firmware changes and losing page-write efficiency.

Availability

AT28HC256-12SU-T is available at Aetrix Electronics and suitable for industrial control systems, medical instrumentation, automotive body electronics, and automated test equipment requiring stable component supply and long-term obsolescence management.

Supply support for AT28HC256-12SU-T 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 is a global semiconductor company specializing in microcontrollers, analog devices, and nonvolatile memory solutions, with emphasis on reliability, longevity, and industrial-grade qualification.

The AT28HC256 belongs to Microchip's high-speed parallel EEPROM product line, engineered for direct SRAM-bus replacement in legacy and new industrial designs requiring robust, low-power, field-updatable nonvolatile storage.

FAQ

What is the maximum write cycle time for AT28HC256-12SU-T during a full-page operation?

The AT28HC256-12SU-T has a maximum page write cycle time of 10 ms. This value applies to all 1–64-byte writes within a single page (defined by A6–A14), and is guaranteed across the full industrial temperature range and 5 V ±10% supply. The device automatically manages internal timing after the first byte is latched, freeing the host bus for other tasks during the write period.

Does AT28HC256-12SU-T support both hardware and software data protection mechanisms?

Yes, AT28HC256-12SU-T integrates dual-layer data protection. Hardware protection includes VCC sensing (<3.8 V disables writes), 5 ms power-on delay, and noise filtering on CE/WE inputs. Software protection uses a three-byte unlock sequence (AAh → 55h → A0h to enable; AAh → 55h → 80h → AAh → 20h → 55h to disable), which persists across power cycles and prevents inadvertent writes in production or field environments.

How does the DATA Polling feature work on AT28HC256-12SU-T?

During a write cycle, reading the last written byte from AT28HC256-12SU-T returns the complement of that data on I/O7. Once the internal programming completes, true data appears on I/O7 and all outputs. This allows the host microcontroller to poll I/O7 asynchronously without fixed delays or external timers-enabling deterministic write completion detection in real-time firmware.

Can AT28HC256-12SU-T be used as a direct replacement for standard SRAM in existing designs?

AT28HC256-12SU-T is functionally compatible with SRAM for read operations and shares the same JEDEC byte-wide pinout, but differs in write behavior: it requires explicit WE/CE/OE sequencing and has finite write endurance. For read-only or infrequent-write use cases, it serves as a drop-in nonvolatile SRAM replacement; however, write-intensive applications require firmware adaptation to manage page writes and polling.

What package type and lead count does AT28HC256-12SU-T use?

AT28HC256-12SU-T is supplied in a 28-lead Small Outline Integrated Circuit (SOIC) package with gull-wing leads, RoHS-compliant green molding compound, and JEDEC-standard pinout. The "U" suffix in the part number explicitly denotes the SOIC package, distinguishing it from the PLCC variant (e.g., AT28HC256-12SU), and supports surface-mount reflow assembly per IPC-J-STD-020.