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Microchip Technology AT28C256-25UM/883

Name: AT28C256-25UM/883
Brand: Microchip Technology
SKU: AT28C256-25UM/883
Price: 2.40 USD
Availability: InStock
Rating: 5 (2 reviews)

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Part No.:: AT28C256-25UM/883

Manufacturer:: Microchip Technology

Category:: Memory

Package:: 28-BCPGA

Datasheet:: AT28C256-25UM/883.pdf

Description:: IC EEPROM 256KBIT PAR 28CPGA

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Product details

Overview

AT28C256-25UM/883 from Microchip Technology is a military-grade paged parallel EEPROM with 256-Kbit (32,768 × 8) organization, 250 ns read access time, single 5V ±10% supply, and JEDEC-approved byte-wide pinout. It supports page write operations of 1–64 bytes with ≤10 ms write cycle time and delivers 300 µA CMOS standby current for low-power embedded systems requiring nonvolatile storage in harsh environments.

For engineers reviewing the AT28C256-25UM/883 datasheet, AT28C256-25UM/883 pinout, AT28C256-25UM/883 application, or AT28C256-25UM/883 equivalent, this device serves as a drop-in replacement for legacy parallel EEPROMs in avionics, missile guidance, and space-qualified telemetry systems where extended temperature operation (−55°C to +125°C), data retention (>10 years), and hardware/software write protection are mandatory.

Technical Context

The AT28C256-25UM/883 implements a paged architecture with an internal 64-byte latch enabling simultaneous multi-byte writes without external timing control. Its dual-line chip enable (CE) and output enable (OE) logic allows flexible bus contention management in shared-memory systems.

It integrates VCC sense circuitry (write inhibit below 3.8 V), 5 ms power-on delay, noise filtering on WE/CE inputs (<15 ns pulse rejection), and optional software data protection (SDP) using three-byte unlock sequences at addresses 5555H/2AAAH/5555H - all verified per MIL-PRF-38535 Class B requirements for the /883 variant.

Key Specifications

Parameter	Value and Actual Design Meaning
Memory Size	256 Kbit (32,768 × 8) - provides full 16-bit addressable nonvolatile storage for firmware boot code or calibration tables.
Read Access Time	250 ns max - meets timing constraints for 4 MHz synchronous bus interfaces in legacy military computing platforms.
Page Write Cycle	≤10 ms - enables efficient field-upgradable parameter sets without system-level timeout penalties.
Operating Temperature	−55°C to +125°C - qualified per MIL-STD-883 Method 1010 for use in sealed avionics enclosures and propulsion control units.
Supply Voltage	5V ±10% - compatible with standard TTL/CMOS logic rails and eliminates need for dedicated voltage regulators.
Standby Current	300 µA CMOS - reduces quiescent power in battery-backed mission-critical subsystems during dormant phases.
Data Retention	10 years minimum - ensures long-term integrity of stored flight profiles, sensor offsets, and cryptographic keys.
Endurance	10,000 write/erase cycles - sufficient for periodic recalibration logging in inertial measurement units (IMUs).

Pinout & Package

AT28C256-25UM/883 is supplied in a 30-pin Ceramic Pin Grid Array (PGA) package compliant with MIL-STD-1835 U-configuration, featuring hermetically sealed construction and lead finish suitable for high-reliability solder reflow profiles.

Pin/Terminal	Circuit Role	Design Meaning
A0–A14	Address Inputs	15-bit address bus supporting full 32K-word addressing; A6–A14 define page boundaries for 64-byte page writes.
I/O0–I/O7	Bi-directional Data Bus	8-bit parallel interface compatible with 8086/80C86 and Z80-based controllers; supports DATA Polling on I/O7 and Toggle Bit on I/O6.
CE	Chip Enable	Active-low selection signal; when high, forces outputs to high-impedance state regardless of OE/WE state - critical for bus isolation.
OE	Output Enable	Active-low read control; must be low during valid read cycles and high during write operations to prevent bus contention.
WE	Write Enable	Active-low write strobe; falling edge latches address/data; combined with CE controls byte vs. page write initiation per AC timing specs.
VCC	Power Supply	+5V ±10% input; includes internal VCC sense circuitry that blocks writes if voltage drops below 3.8 V typical.
GND	Ground Reference	Signal return path; pin 14 in 30-pin PGA layout - requires low-inductance connection to minimize noise coupling during write cycles.
DC (Pins 1, 17)	Don't Connect	No internal connection; must remain unconnected per CLCC package marking note - violation risks latch-up or parametric shift.

Key Features

Feature	Design Value
Hardware Write Protection	VCC sense + 5 ms power-on delay + noise filtering ensures zero inadvertent writes during brown-out or EMI transients.
Software Data Protection (SDP)	Three-byte unlock sequence (AAH/55H/A0H) enables selective write-enable per memory region - prevents corruption of critical configuration sectors.
DATA Polling & Toggle Bit	Real-time write completion detection via I/O7 complement or I/O6 toggling - eliminates need for fixed delays or external timers in host firmware.
Page Write Architecture	Internal 64-byte latch allows burst loading of up to 64 bytes within 150 µs intervals - improves throughput by 64× over byte-write mode.
MIL-PRF-38535 Class B Qualification	Full screening including burn-in, temperature cycling, and radiation hardness assurance - required for DoD procurement in flight-critical systems.
Device Identification Area	64-byte reserved sector (7FC0H–7FFFH) accessible at 12 V on A9 - supports unique unit serialization and traceability per MIL-STD-130.

Applications

Avionics Boot Memory	Missile Guidance Calibration Storage
Use Scenario: Storing bootloader firmware and FPGA configuration bitstreams in airborne mission computers operating across −55°C to +125°C. IC Role / Device Role / Timing Role: Nonvolatile program memory mapped into CPU address space; accessed as SRAM-equivalent during power-up initialization. Use Value: 250 ns read access ensures deterministic boot timing; MIL-883 qualification guarantees reliability under vibration and thermal shock.	Use Scenario: Holding real-time gyro bias compensation coefficients updated during pre-launch alignment in tactical missiles. IC Role / Device Role / Timing Role: Parameter storage element interfaced to ADC/DAC subsystems; written via page mode during maintenance windows. Use Value: 10,000-cycle endurance exceeds field life requirements; software data protection prevents accidental overwrite during test mode transitions.
Satellite Telemetry Logger	Nuclear Power Plant Control Interface
Use Scenario: Recording radiation-hardened sensor readings and command logs in LEO satellite payloads with 10-year orbital lifetime. IC Role / Device Role / Timing Role: Persistent data buffer synchronized to housekeeping telemetry frames; powered from regulated 5V bus. Use Value: 10-year data retention eliminates need for periodic refresh; 300 µA standby current extends battery life between ground contacts.	Use Scenario: Storing safety-critical trip setpoints and reactor coolant pump calibration constants in Class 1E nuclear instrumentation channels. IC Role / Device Role / Timing Role: Fail-safe configuration store accessed only during maintenance; isolated via optocoupled address/data buses. Use Value: Hermetic 30-pin PGA packaging resists moisture ingress in humid containment buildings; VCC sense prevents writes during grid instability.

Avionics Boot Memory

Missile Guidance Calibration Storage

Use Scenario: Storing bootloader firmware and FPGA configuration bitstreams in airborne mission computers operating across −55°C to +125°C.

IC Role / Device Role / Timing Role: Nonvolatile program memory mapped into CPU address space; accessed as SRAM-equivalent during power-up initialization.

Use Value: 250 ns read access ensures deterministic boot timing; MIL-883 qualification guarantees reliability under vibration and thermal shock.

Use Scenario: Holding real-time gyro bias compensation coefficients updated during pre-launch alignment in tactical missiles.

IC Role / Device Role / Timing Role: Parameter storage element interfaced to ADC/DAC subsystems; written via page mode during maintenance windows.

Use Value: 10,000-cycle endurance exceeds field life requirements; software data protection prevents accidental overwrite during test mode transitions.

Satellite Telemetry Logger

Nuclear Power Plant Control Interface

Use Scenario: Recording radiation-hardened sensor readings and command logs in LEO satellite payloads with 10-year orbital lifetime.

IC Role / Device Role / Timing Role: Persistent data buffer synchronized to housekeeping telemetry frames; powered from regulated 5V bus.

Use Value: 10-year data retention eliminates need for periodic refresh; 300 µA standby current extends battery life between ground contacts.

Use Scenario: Storing safety-critical trip setpoints and reactor coolant pump calibration constants in Class 1E nuclear instrumentation channels.

IC Role / Device Role / Timing Role: Fail-safe configuration store accessed only during maintenance; isolated via optocoupled address/data buses.

Use Value: Hermetic 30-pin PGA packaging resists moisture ingress in humid containment buildings; VCC sense prevents writes during grid instability.

Equivalent & Alternatives

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

Alternative Part	Technical Difference	Application Difference	Selection Advice
AT28C256-25JM/883	Same die, 32-pin CERDIP package instead of 30-pin PGA; identical AC/DC specs and MIL-883 screening.	Requires PCB redesign due to different pin count, footprint, and thermal mass - unsuitable for drop-in replacement in existing PGA layouts.	Select only when board-level redesign accommodates CERDIP mechanical constraints and thermal dissipation profile.
DS2502-E48+T&R	1-Wire serial EEPROM (48-bit ID + 1024-bit user memory); no parallel interface, no page write, 5V-only operation.	Limited to low-bandwidth configuration storage; incompatible with address/data bus architectures requiring byte/page random access.	Choose only for new designs prioritizing minimal pin count and daisy-chain capability over speed and capacity.

Compared with AT28C256-25UM/883, the AT28C256-25JM/883 offers identical functionality in a different hermetic package, while DS2502-E48+T&R sacrifices parallel performance and capacity for serial simplicity - making AT28C256-25UM/883 the sole choice for legacy-mandated parallel bus integration in certified military platforms.

Availability

AT28C256-25UM/883 is available at Aetrix Electronics and suitable for avionics boot memory, missile guidance calibration storage, satellite telemetry logging, and nuclear power plant control interface applications requiring stable component supply across extended product lifecycles.

Supply support for AT28C256-25UM/883 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 for industrial, automotive, and aerospace markets.

The AT28C256 product line was developed to deliver radiation-tolerant, high-endurance parallel EEPROMs for mission-critical systems where data integrity under extreme environmental stress is non-negotiable.

FAQ

What is the maximum operating temperature range for the AT28C256-25UM/883?

The AT28C256-25UM/883 is fully qualified for operation from −55°C to +125°C per MIL-STD-883 Method 1010. This range is validated through temperature cycling, steady-state burn-in, and parametric testing across the full span - ensuring reliable read/write functionality in jet engine bays, missile canisters, and spacecraft thermal vacuum environments. The AT28C256-25UM/883 maintains specified tACC ≤250 ns and ICC ≤50 mA throughout this range.

Does the AT28C256-25UM/883 support page write operations, and what is the maximum page size?

Yes, the AT28C256-25UM/883 supports page write operations with a maximum page size of 64 bytes. The device uses an internal address and data latch to accept sequential bytes within 150 µs (tBLC) of each other; all bytes must reside on the same page defined by A6–A14. Page write cycle time is ≤10 ms, and the AT28C256-25UM/883 automatically manages internal timing without external strobes or clocks.

How does hardware write protection function on the AT28C256-25UM/883?

Hardware write protection on the AT28C256-25UM/883 operates through four independent mechanisms: (1) VCC sense circuitry inhibits writes below 3.8 V, (2) a 5 ms internal power-on delay timer blocks writes until supply stabilizes, (3) write is disabled if OE is low or CE is high, and (4) noise filters reject WE/CE pulses <15 ns. These features are hardwired and active at all times - no software configuration required - and are verified per MIL-PRF-38535 Class B screening.

Can the AT28C256-25UM/883 be used as a direct replacement for older AT28C256 variants in existing designs?

Yes, the AT28C256-25UM/883 is pin-compatible and functionally identical to other AT28C256-25x/883 variants (e.g., -25JM/883, -25LM/883) in terms of electrical characteristics, timing, and JEDEC byte-wide pinout. However, the 30-pin PGA package requires matching socket or footprint - it is not mechanically interchangeable with 28-pin CERDIP or 32-pin CLCC versions. The AT28C256-25UM/883 retains identical AC/DC specs and MIL-883 screening level.

What methods does the AT28C256-25UM/883 provide for detecting write completion?

The AT28C256-25UM/883 provides two hardware-verified methods: (1) DATA Polling - reading the last written byte returns its complement on I/O7 until completion, then true data; and (2) Toggle Bit - I/O6 toggles between 0 and 1 during write, then stabilizes to valid data. Both methods are characterized per Table 6-5 and Table 6-6 and require no additional components - the AT28C256-25UM/883 handles all timing internally.

AT28C256-25UM/883 Specifications

Product attributes: Attribute value

Manufacturer:: Microchip Technology

Series:: -

Package/Case:: 28-BCPGA

Packaging:: Box

Product Status:: Active

Programmable:: Not Verified

Memory Type:: Non-Volatile

Memory Format:: EEPROM

Technology:: EEPROM

Memory Size:: 256Kbit

Memory Organization:: 32K x 8

Memory Interface:: Parallel

Clock Frequency:: -

Write Cycle Time - Word, Page:: 10ms

Access Time:: 250 ns

Voltage - Supply:: 4.5V ~ 5.5V

Operating Temperature:: -55°C ~ 125°C (TC)

Grade:: -

Qualification:: -

Mounting Type:: Through Hole

Supplier Device Package:: 28-CPGA (13.97x16.51)

AT28C256-25UM/883 FAQ

1.How can I place an order for AT28C256-25UM/883 through Aetrix?

Please submit a Request for Quotation (RFQ) for AT28C256-25UM/883 on Aetrix. Our sales agent will provide a competitive quotation and guide you through the order confirmation once you accept the terms.

2.Are the price and stock information for AT28C256-25UM/883 reliable?

The price and inventory of AT28C256-25UM/883 are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for AT28C256-25UM/883 is usually 5 days.

3.What payment methods are accepted for AT28C256-25UM/883?

We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for AT28C256-25UM/883 transactions.

Note: Certain payment methods may incur a processing fee.

4.How is shipping managed for AT28C256-25UM/883?

AT28C256-25UM/883 orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.

Once your AT28C256-25UM/883 order is processed, you will receive an email with the shipment details and tracking number.

Note: Tracking information may take up to 24 hours to appear. Express delivery typically takes 3–5 business days.

5.How can I obtain technical support or documentation for AT28C256-25UM/883?

For technical support, including AT28C256-25UM/883 datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your AT28C256-25UM/883 requirements.

6.How does Aetrix verify that AT28C256-25UM/883 is sourced from the original manufacturer or authorized distributors?

All AT28C256-25UM/883 products on Aetrix are procured from qualified distributors and authorized channels. Our dedicated quality assurance team conducts strict verification, including traceability checks and, if necessary, third-party testing. This ensures that AT28C256-25UM/883 meets industry standards.

7.What is the process for return or replacement of AT28C256-25UM/883?

All AT28C256-25UM/883 units undergo pre-shipment inspection (PSI). If there is an issue with AT28C256-25UM/883, returns or replacements are accepted under the following conditions:

1.Quantity discrepancies, incorrect items, or visible external defects (such as breakage or corrosion), acknowledged by Aetrix.

2.The issue is reported within 90 days of delivery.

3.The AT28C256-25UM/883 part is unused and in its original packaging.

Return procedure for AT28C256-25UM/883:

1.Submit a request within 90 days.

2.Obtain a Return Material Authorization (RMA) from Aetrix.

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