Microchip Technology AT27C256R-45RC

Overview

AT27C256R-45RC from Atmel is a 32K × 8-bit one-time programmable EPROM with 45 ns read access time, 5V ±10% supply operation, and JEDEC-standard 28-lead SOIC package. It serves as non-volatile firmware storage in microprocessor systems, enabling direct byte-access without wait states and supporting rapid programming at 100 µs/byte.

For engineers reviewing the AT27C256R-45RC datasheet, AT27C256R-45RC pinout, AT27C256R-45RC application, or AT27C256R-45RC equivalent, key selection criteria include read timing (tACC ≤ 45 ns), standby current (≤100 µA), VPP programming voltage (12.0 V ±0.5 V), and compatibility with TTL/CMOS bus interfaces in embedded control and legacy system upgrades.

Technical Context

The AT27C256R-45RC implements a two-line control architecture using CE and OE to manage output enable and chip select independently, preventing bus contention during multi-device memory mapping. Its CMOS process delivers latchup immunity (200 mA) and ESD protection (2,000 V), while the Rapid™ Programming Algorithm enables verified byte programming in ≤100 µs per byte under 13.0 V VPP and 6.5 V VCC.

It supports product identification via A9 and A0 toggling to read manufacturer (0x1E) and device code (0x8C) bytes, and operates across commercial temperature range (0°C to 70°C). The device requires no external clock and uses standard parallel address/data bus interfacing with 15 address lines (A0–A14) and 8 bidirectional data outputs (O0–O7).

Key Specifications

Pinout & Package

AT27C256R-45RC is housed in a 28-lead SOIC (28R) package per JEDEC MS-012 standard, 0.330" wide, gull-wing lead form, with 1.27 mm pitch and surface-mount compatibility.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar OTP EPROM applications.

Compared with AT27C256R-45RC, the AT27C256B-45RC offers enhanced manufacturing consistency without layout or timing changes, while MX27C256-45PC trades SOIC space efficiency and ID features for through-hole compatibility and broader distributor availability.

Availability

AT27C256R-45RC is available at Aetrix Electronics and suitable for legacy system repair, industrial controller upgrades, and embedded instrumentation requiring stable component supply with full traceability and long-term obsolescence management.

Supply support for AT27C256R-45RC 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 was a U.S.-based semiconductor designer specializing in microcontrollers, non-volatile memory, and secure authentication ICs before its acquisition by Microchip Technology in 2016.

The AT27C256R-45RC belongs to Atmel's OTP EPROM product line, engineered for reliable, low-risk firmware storage in cost-sensitive, long-lifecycle embedded systems where reprogrammability is unnecessary or undesirable.

FAQ

What is the maximum operating temperature range for the AT27C256R-45RC?

The AT27C256R-45RC is specified for commercial temperature operation from 0°C to 70°C. This range is explicitly defined in the Ordering Information table and applies to all electrical and timing parameters unless otherwise noted. It is not rated for industrial (−40°C to +85°C) or automotive (−40°C to +125°C) use - those variants carry suffixes like "-45RI" or "-45RA". The AT27C256R-45RC must be used within its stated 0°C–70°C envelope to guarantee tACC ≤ 45 ns and ISB ≤ 100 µA performance.

Can the AT27C256R-45RC be programmed in-circuit?

No, the AT27C256R-45RC cannot be reliably programmed in-circuit. Programming requires VPP = 12.0 V ±0.5 V applied to pin 1, which exceeds standard 5V system rails and risks damaging adjacent components. The datasheet mandates external programming equipment with precise voltage control, 0.1 µF VPP-to-GND decoupling, and strict timing (e.g., tPW = 95–105 µs). In-system programming is unsupported; the AT27C256R-45RC must be removed and programmed on a dedicated EPROM writer before soldering.

Does the AT27C256R-45RC require external pull-up resistors on its output pins?

No, the AT27C256R-45RC does not require external pull-up resistors on O0–O7. Its outputs are actively driven CMOS-compatible buffers with VOH ≥ 2.4 V at IOH = −400 µA and VOL ≤ 0.4 V at IOL = 2.1 mA, meeting TTL and CMOS logic thresholds directly. Pull-ups would interfere with bus contention management and violate the two-line control (CE/OE) architecture designed for shared-data-bus operation.

What is the purpose of the NC pins on the AT27C256R-45RC SOIC package?

The AT27C256R-45RC SOIC package has no NC (No Connect) pins - all 28 pins are assigned functions per the PDIP/SOIC top-view diagram: pins 1 (VPP), 10 (GND), 20 (VCC), and 28 (NC) are explicitly labeled, but pin 28 is designated NC only in PLCC and TSOP variants. In the 28R (SOIC) package, pin 28 is VCC. Therefore, no pins on the AT27C256R-45RC SOIC variant are NC; mislabeling may arise from cross-referencing other package drawings. Always verify against the SOIC-specific pinout on page 2 of the datasheet.

How is the Integrated Product Identification Code read from the AT27C256R-45RC?

The Integrated Product Identification Code is read by asserting CE = VIL and OE = VIL while setting A9 = VH (12.0 V ±0.5 V) and toggling A0 between VIL and VIH; all other address lines (A1–A14) must be held low. When A0 = VIL, the Manufacturer ID byte (0x1E) appears on O0–O7; when A0 = VIH, the Device Code byte (0x8C) appears. This sequence requires a dedicated 12 V source on A9 and is supported only by compliant EPROM programmers - it cannot be executed using standard 5 V microcontroller GPIO.