Microchip Technology AT28BV256-20SC

Overview

AT28BV256-20SC from Atmel is a 256 Kbit (32K × 8) parallel EEPROM operating from a single 2.7V–3.6V supply, featuring 200 ns read access time, 10 ms maximum page write cycle, JEDEC-standard byte-wide pinout, and hardware/software data protection. It serves as nonvolatile program/data storage in embedded controllers, industrial PLCs, and telecom line cards requiring battery-voltage operation and field-upgradable firmware.

For engineers reviewing the AT28BV256-20SC datasheet, AT28BV256-20SC pinout, AT28BV256-20SC application, or AT28BV256-20SC equivalent, key selection criteria include its 200 ns read timing, 64-byte page write capability, CMOS standby current of 20 µA, DATA polling/Toggle Bit write completion detection, and compatibility with standard SRAM bus interfaces without external logic.

Technical Context

The AT28BV256-20SC implements a parallel interface with CE/OE/WE control logic enabling SRAM-like read/write cycles. Its internal 64-byte page register latches address and data during page writes, decoupling the host bus for concurrent operations while an internal timer manages autonomous programming.

Write completion is verified via dual methods: DATA polling on I/O7 (complement-to-data then true data) and Toggle Bit behavior on I/O6 (toggling until write ends). Hardware protection includes VCC power-on delay (~10 ms), noise filtering (<15 ns pulse rejection), and write-inhibit states; software protection requires a three-byte unlock sequence before each write operation.

Key Specifications

Pinout & Package

AT28BV256-20SC uses a 28-pin SOIC (28S) package per JEDEC MS-013, 0.300" body width, with 1.27 mm pitch. Pin 1 is marked by a beveled corner; pins 1–14 and 15–28 are on opposing sides. NC pins (A11, A12, A14 in some configurations) are not internally connected and must remain unconnected.

Key Features

Applications

Equivalent & Alternatives

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

Compared with ST M28W256F and Microchip 25LC256, the AT28BV256-20SC delivers faster deterministic write completion via dual-status signaling, JEDEC-compatible pinout for legacy design reuse, and integrated 64-byte ID space-making it optimal for SRAM-bus-based industrial and telecom systems requiring field firmware updates and calibration persistence.

Availability

AT28BV256-20SC is available at Aetrix Electronics and suitable for industrial PLCs, telecom line cards, medical diagnostics, automotive body control modules, and embedded instrumentation requiring stable component supply with guaranteed long-term availability.

Supply support for AT28BV256-20SC 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

Atmel Corporation (now part of Microchip Technology) was a U.S.-based semiconductor company specializing in microcontrollers, nonvolatile memory, and security ICs, known for robust industrial-grade products and long-lifecycle support.

The AT28BV256 series belongs to Atmel's battery-voltage parallel EEPROM product line, designed specifically for reliable, low-power, field-upgradable nonvolatile storage in systems constrained by 3.3V rails and demanding extended data retention.

FAQ

What is the maximum page write size supported by the AT28BV256-20SC?

The AT28BV256-20SC 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 a single write cycle. All bytes written in one page operation must reside on the same page, defined by address bits A6–A14. The AT28BV256-20SC enforces this boundary strictly-exceeding the 64-byte limit or crossing page boundaries mid-write will terminate the operation and initiate internal programming.

Does the AT28BV256-20SC require a 12V supply for normal operation?

No, the AT28BV256-20SC operates exclusively from a 2.7V–3.6V supply for all standard read, write, and erase functions. A 12V ±0.5V supply on pin A9 is required only for accessing the optional 64-byte device identification area (7FC0H–7FFFH); this is a one-time or infrequent operation and not part of routine firmware or configuration storage. The AT28BV256-20SC contains an internal charge pump that generates necessary high voltages for programming from the 3.3V rail.

How does hardware write protection work on the AT28BV256-20SC?

Hardware write protection on the AT28BV256-20SC operates through three mechanisms: (1) a VCC power-on delay (~10 ms after VCC reaches 1.8V) prevents writes during power ramp-up; (2) write inhibition occurs if any of OE is low, CE is high, or WE is high; and (3) input noise filtering rejects pulses <15 ns on CE or WE. These features ensure the AT28BV256-20SC remains immune to spurious writes during system power transitions or EMI events without software intervention.

Can the AT28BV256-20SC be used as a direct replacement for a 27C256 EPROM?

Yes, the AT28BV256-20SC features a JEDEC-approved byte-wide pinout identical to the 27C256 EPROM, including matching A0–A14, I/O0–I/O7, CE, OE, and WE pin assignments. However, unlike UV-erasable EPROMs, the AT28BV256-20SC supports in-system electrical erasure and writing. To replace a 27C256, ensure the host system provides proper write enable sequencing and respects the AT28BV256-20SC's software unlock requirement for writes.

What is the purpose of the Toggle Bit feature on the AT28BV256-20SC?

The Toggle Bit feature on the AT28BV256-20SC uses I/O6 to signal write completion: during an active write cycle, successive reads cause I/O6 to toggle between 0 and 1; once the write finishes, I/O6 stabilizes and valid data appears on all outputs. This provides a second, independent method-alongside DATA polling on I/O7-for detecting write end without fixed delays. The AT28BV256-20SC guarantees this behavior across all temperature ranges and supply voltages within spec.