Microchip Technology AT28HC256-70TU

Overview

AT28HC256-70TU from Microchip Technology is a military-grade 256-Kbit (32,768 × 8) paged parallel EEPROM with 90 ns read access time, 3–10 ms page write cycle, and full operation across –55°C to +125°C. It features hardware/software data protection, DATA polling and toggle-bit write completion detection, and JEDEC-standard byte-wide pinout for embedded avionics and ruggedized control systems.

For engineers reviewing the AT28HC256-70TU datasheet, AT28HC256-70TU pinout, AT28HC256-70TU application, or AT28HC256-70TU equivalent, key selection considerations include military temperature compliance, 64-byte page write capability, VCC sense-based write inhibit, 10,000/100,000 endurance cycles, and compatibility with TTL/CMOS bus interfaces in high-reliability memory subsystems.

Technical Context

The AT28HC256-70TU implements a paged architecture with an internal 64-byte latch enabling simultaneous writes of 1–64 bytes within a single page (A6–A14 fixed), reducing bus occupancy versus byte-by-byte programming. Its dual-line chip enable (CE) and output enable (OE) control supports flexible bus contention management in multi-device systems.

Write completion is verified via I/O7 DATA polling (complement-to-data feedback) or I/O6 toggle-bit behavior-both operable at any point during tWC-eliminating need for fixed delay timers. Hardware write protection includes VCC sense (<3.8 V inhibition), 5 ms power-on delay, noise filtering (<15 ns pulse rejection), and CE/OE/WE logic gating.

Key Specifications

Pinout & Package

AT28HC256-70TU is supplied in a 32-lead CERDIP (Ceramic Dual In-line Package) with 0.600" width, hermetically sealed per MIL-STD-1835 D-10 Config A. Pin 1 is index-corner marked; pins 1 and 17 are "Don't Connect" (DC) per CLCC variant but not present in CERDIP - this package uses standard 32-pin mapping with no NC pins.

Key Features

Applications

Equivalent & Alternatives

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

Compared with AT28HC256-70TU, AT28C256-15PU sacrifices military temperature range and write-protection robustness for lower cost, while MX28F256J3F replaces EEPROM's instant-write capability with flash's higher density and endurance at the expense of deterministic latency and byte-level update flexibility.

Availability

AT28HC256-70TU is available at Aetrix Electronics and suitable for avionics, defense vehicle control, spacecraft payload configuration, and ruggedized industrial PLC applications requiring stable component supply across extended product lifecycles.

Supply support for AT28HC256-70TU 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 U.S.-based semiconductor manufacturer specializing in microcontrollers, analog devices, and nonvolatile memory solutions for aerospace, defense, and industrial markets.

The AT28HC256-70TU belongs to Microchip's military-qualified parallel EEPROM product line, designed specifically for high-reliability, long-lifecycle applications where data integrity under extreme thermal and electrical stress is mandatory.

FAQ

What is the maximum page write size supported by the AT28HC256-70TU?

The AT28HC256-70TU supports a maximum page write size of 64 bytes. This is enabled by its internal 64-byte page register, which latches address and data during the initial write strobe. All bytes written within a single page operation must reside on the same page, defined by address bits A6–A14, and each successive byte must be loaded within 150 µs of the previous one to avoid premature internal write initiation. The AT28HC256-70TU does not support larger burst writes beyond this limit.

Does the AT28HC256-70TU require external high-voltage programming signals?

No, the AT28HC256-70TU operates from a single 5 V ±10% supply and does not require external high-voltage programming signals for standard byte or page writes. Only the optional Chip Erase mode (using a 6-byte software sequence) and Device Identification memory programming require 12.0 V ±0.5 V applied to A9 - all other write operations, including those protected by Software Data Protection, use standard 5 V signaling. The AT28HC256-70TU integrates VCC sensing to inhibit writes below ~3.8 V, eliminating need for external HV generators in normal operation.

How is write completion detected on the AT28HC256-70TU without using a timer?

Write completion on the AT28HC256-70TU is detected using two hardware-supported methods: DATA polling on I/O7 and toggle-bit monitoring on I/O6. During a write, reading the last-written address returns the complement of the data on I/O7 until completion, then true data. Alternatively, I/O6 toggles between 0 and 1 on successive reads and stops toggling once the write finishes. Both methods are asynchronous and can be initiated at any time during tWC - no fixed delay or external timer is needed. These mechanisms are integral to the AT28HC256-70TU's design and require no additional components.

What packaging variants are available for the AT28HC256-70TU, and what does "-70TU" signify?

The "-70TU" suffix indicates a 32-lead CERDIP package with 90 ns access time and military temperature range (–55°C to +125°C). While the AT28HC256 family is offered in 32-lead CERDIP, 32-lead CLCC, 32-lead Flatpack, and 30-pin PGA packages, the -70TU designation specifically refers to the CERDIP variant. The "70" denotes 90 ns speed grade (per Microchip's legacy marking: 70 = 90 ns, 12 = 120 ns), and "TU" identifies the CERDIP package per Microchip's ordering code system. Other variants use different suffixes (e.g., -70LU for CLCC).

Can the AT28HC256-70TU be used as a direct replacement for SRAM in existing designs?

Yes, the AT28HC256-70TU can function as a read-compatible SRAM replacement due to its identical byte-wide JEDEC pinout and SRAM-like read timing (90 ns access, CE/OE-controlled outputs). However, write operations differ fundamentally: writes require explicit WE strobing and status verification (via DATA polling or toggle bit), unlike SRAM's transparent write. The AT28HC256-70TU also draws active current during writes and has finite endurance, so it is suitable only where firmware can accommodate non-transparent write protocols and lifetime write counts remain within 10,000–100,000 cycles.