Microchip Technology AT28C256-20DM/883

Overview

AT28C256-20DM/883 from Microchip Technology is a military-grade 256-Kbit (32,768 × 8) paged parallel EEPROM with 200 ns read access time, JEDEC-standard byte-wide pinout, and single 5V ±10% supply operation. It supports 1–64-byte page writes 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 AT28C256-20DM/883 datasheet, AT28C256-20DM/883 pinout, AT28C256-20DM/883 application, or AT28C256-20DM/883 equivalent, this device serves as a drop-in replacement for legacy parallel EEPROMs in avionics, missile guidance, and space-qualified instrumentation where extended temperature range (−55°C to +125°C), hardware/software data protection, and 10-year data retention are mandatory.

Technical Context

The AT28C256-20DM/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 arbitration in shared-memory systems, while DATA Polling on I/O7 and Toggle Bit on I/O6 provide deterministic end-of-write detection independent of system clock.

Hardware write protection includes VCC sense (<3.8 V inhibits write), 5 ms power-on delay, noise filtering (<15 ns pulse rejection), and CE/OE/WE state monitoring. Software Data Protection (SDP) uses a 3-byte unlock sequence (AAh/55h/A0h) to guard against inadvertent writes, with SDP disabled at factory shipment and persistent across power cycles.

Key Specifications

Pinout & Package

AT28C256-20DM/883 is supplied in a 32-lead CERDIP (Dual In-line Package) with ceramic hermetic seal, compliant with MIL-STD-1835 D-10 Config A and rated for high-reliability military applications. Pin 1 is marked by notch or dot; pins 1 and 17 are "Don't Connect" (DC) per CLCC variant mapping, but unused in CERDIP.

Key Features

Applications

Equivalent & Alternatives

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

Compared with AT28C256-20DM/883, the LM/883 variant offers superior thermal performance in conduction-cooled modules, while the FM/883 maintains pin-for-pin compatibility with older flatpack-based avionics racks - both retain identical 200 ns read timing, 10 ms page write, and MIL-PRF-38535 Class B qualification.

Availability

AT28C256-20DM/883 is available at Aetrix Electronics and suitable for avionics flight control, missile guidance systems, spacecraft telemetry recorders, and nuclear submarine sonar processors requiring stable component supply under extended temperature and radiation-exposed conditions.

Supply support for AT28C256-20DM/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 Inc. is a global semiconductor company specializing in microcontrollers, analog devices, and nonvolatile memory solutions for aerospace, defense, and industrial markets.

The AT28C256 product line was developed to deliver radiation-tolerant, high-reliability parallel EEPROMs for mission-critical systems where data integrity across extreme thermal, mechanical, and electromagnetic stressors is non-negotiable.

FAQ

What is the maximum page write size supported by the AT28C256-20DM/883?

The AT28C256-20DM/883 supports a maximum page write size of 64 bytes. This is enabled by its internal 64-byte page register, which latches sequential data bytes within a 150 µs window (tBLC). Each byte must reside on the same page defined by address bits A6–A14, and the page write cycle completes automatically in ≤10 ms without external timing control. The AT28C256-20DM/883 does not require external hardware to manage page boundaries or write timing.

How does hardware write protection function on the AT28C256-20DM/883?

Hardware write protection on the AT28C256-20DM/883 operates through four mechanisms: (1) VCC sense circuitry disables writes if supply drops below 3.8 V, (2) a 5 ms internal power-on delay prevents writes until stable operation is confirmed, (3) write inhibition occurs if OE is low, CE is high, or WE is high, and (4) input noise filters reject pulses <15 ns on CE or WE. These features ensure the AT28C256-20DM/883 remains immune to spurious writes during power sequencing or EMI events in military platforms.

Can the AT28C256-20DM/883 be used as a direct replacement for standard 27C256 EPROMs?

Yes, the AT28C256-20DM/883 uses JEDEC-approved byte-wide pinout and shares identical address/data bus assignments with 27C256 EPROMs, enabling drop-in replacement in existing sockets. However, unlike EPROMs, the AT28C256-20DM/883 requires no UV erasure and supports in-system electrical reprogramming. Its 200 ns read access matches 27C256-20 variants, and the AT28C256-20DM/883 maintains full compatibility with standard 5V TTL/CMOS logic levels and timing interfaces.

What is the purpose of the extra 64-byte memory area in the AT28C256-20DM/883?

The AT28C256-20DM/883 includes an additional 64-byte EEPROM segment (addresses 7FC0h–7FFFh) accessible only when A9 is raised to 12.0 V ± 0.5 V. This area is reserved for device identification, calibration data storage, or firmware version tracking - separate from main memory to prevent accidental overwrite. It supports the same 10,000-cycle endurance and 10-year retention as the primary array, and the AT28C256-20DM/883 allows independent read/write operations to this region without affecting user memory contents.

Does the AT28C256-20DM/883 support chip erase functionality?

Yes, the AT28C256-20DM/883 supports optional software-controlled chip erase using a 6-byte command sequence applied under 12.0 V ± 0.5 V on A9. This operation clears all 32,768 bytes to FFh in a single action, distinct from page or byte writes. Chip erase timing requires ≥10 ms (tW) with specific setup/hold constraints on CE, OE, and WE, and the AT28C256-20DM/883 retains full MIL-PRF-38535 Class B qualification even when executing this mode.