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Home > Products > Integrated Circuits (ICs) > Memory > Memory

Microchip Technology 27C256-25/SO277

Name: 27C256-25/SO277
Brand: Microchip Technology
SKU: 27C256-25/SO277
Price: 2.40 USD
Availability: InStock
Rating: 5 (2 reviews)

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Part No.:: 27C256-25/SO277

Manufacturer:: Microchip Technology

Category:: Memory

Package:: 28-SOIC (0.295", 7.50mm Width)

Datasheet:: 27C256-25/SO277.pdf

Description:: IC EPROM 256KBIT PARALLEL 28SOIC

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Product details

Overview

27C256-25/SO277 from Microchip Technology is a 32K × 8-bit UV-erasable EPROM with 25 ns access time, 5 V supply voltage, and SOIC-28 surface-mount package. It serves as non-volatile program storage in legacy microcontroller systems, industrial controllers, and boot ROM applications requiring field-programmable read-only memory.

For engineers reviewing the 27C256-25/SO277 datasheet, 27C256-25/SO277 pinout, 27C256-25/SO277 application, or 27C256-25/SO277 equivalent, key selection factors include verified 25 ns read timing, UV-erase cycle compatibility, SOIC-28 footprint compliance, and TTL/CMOS input/output logic levels.

Technical Context

This EPROM implements standard NMOS floating-gate technology with address latch enable (ALE) control for multiplexed bus interfacing. It supports full 16-bit address decoding (A0–A15), eight bidirectional data lines (I/O0–I/O7), and active-low chip enable (CE̅) and output enable (OE̅) controls.

Operation requires +5 V ±10% V_CC, with standby current ≤100 mA and active read current ≤150 mA. Programming uses 12.5 V V_PP on pin 1, and erasure requires ≥20-minute exposure to 253.7 nm UV light through the quartz window.

Key Specifications

Parameter	Value and Actual Design Meaning
Memory size	32K × 8 bits = 262,144 bits; sufficient for firmware images up to 32 KB in 8-bit microcontroller boot loaders
Access time	25 ns maximum; enables direct interface with 20 MHz Z80, 8085, or 6502-based systems without wait states
Supply voltage	+5 V ±10%; compatible with legacy TTL logic families and unregulated 5 V power rails
Programming voltage	12.5 V on V_PP (pin 1); requires dedicated EPROM programmer with high-voltage pulse capability
UV erase time	≥20 minutes under 253.7 nm UV source; ensures complete charge depletion from floating gate
Operating temperature	0 °C to +70 °C; validated for commercial-grade embedded control environments

Pinout & Package

27C256-25/SO277 is housed in a 28-pin Small Outline Integrated Circuit (SOIC-28) package with 300-mil body width and standard JEDEC MS-012AC dimensions. Pin pitch is 1.27 mm, and lead finish is matte tin.

Pin/Terminal	Circuit Role	Design Meaning
A0–A14	Address inputs	15-bit address bus for selecting one of 32K memory locations
A15	Address input / V_PP during programming	Selects upper/lower 16K block; repurposed as 12.5 V programming voltage input
I/O0–I/O7	Bidirectional data bus	8-bit parallel data path for read/write operations; TTL-compatible I/O levels
CE̅	Chip enable (active low)	Global device select; disables outputs and reduces power when deasserted
OE̅	Output enable (active low)	Controls data bus drivers; allows shared bus operation with other peripherals
V_CC	Power supply	+5 V supply for core logic and output drivers
GND	Ground reference	Signal and power return path; must be low-impedance for noise immunity
V_PP	Programming voltage	12.5 V input only during programming; not connected during normal operation

Key Features

Feature	Design Value
UV-erasable architecture	Enables reprogramming after device removal and UV exposure-no soldering required for firmware updates
25 ns access time	Supports zero-wait-state operation with 20 MHz CPU buses, reducing system latency
SOIC-28 package	Surface-mount form factor compatible with automated PCB assembly and space-constrained legacy designs
TTL/CMOS-compatible I/O	Interoperates directly with 74LS, 74HC, and microcontroller GPIO without level-shifting circuitry
Single +5 V supply	Eliminates need for dual-rail or high-voltage auxiliary supplies in target systems

Applications

Industrial PLC Firmware Storage	Legacy Microcontroller Boot ROM
Use Scenario: Fixed-function programmable logic controllers use EPROM to store ladder logic execution firmware that rarely changes but must survive power loss. IC Role / Device Role / Timing Role: Non-volatile program memory holding initialization code and runtime instruction set. Use Value: Retains firmware across decades without battery backup; UV-erase allows field updates during maintenance cycles.	Use Scenario: Z80- or 6502-based embedded systems require boot code that loads from ROM before initializing RAM and peripherals. IC Role / Device Role / Timing Role: Primary boot vector memory mapped at reset address 0x0000. Use Value: 25 ns access time eliminates wait states, enabling deterministic boot timing critical for real-time startup.
Test Equipment Configuration Memory	Avionics Maintenance Interface ROM
Use Scenario: Automated test equipment stores calibration constants, test sequence definitions, and instrument configuration tables. IC Role / Device Role / Timing Role: Read-only data storage accessed during self-test and setup phases. Use Value: SOIC-28 footprint allows replacement without board redesign; UV-erase supports recalibration data updates between deployments.	Use Scenario: Ground-support avionics tools embed diagnostic routines and protocol translators in fixed ROM for aircraft subsystem verification. IC Role / Device Role / Timing Role: Dedicated firmware module executing serial command parsing and hardware register initialization. Use Value: Commercial temperature range (0 °C to +70 °C) meets hangar and lab environmental requirements without derating.

Industrial PLC Firmware Storage

Legacy Microcontroller Boot ROM

Use Scenario: Fixed-function programmable logic controllers use EPROM to store ladder logic execution firmware that rarely changes but must survive power loss.

IC Role / Device Role / Timing Role: Non-volatile program memory holding initialization code and runtime instruction set.

Use Value: Retains firmware across decades without battery backup; UV-erase allows field updates during maintenance cycles.

Use Scenario: Z80- or 6502-based embedded systems require boot code that loads from ROM before initializing RAM and peripherals.

IC Role / Device Role / Timing Role: Primary boot vector memory mapped at reset address 0x0000.

Use Value: 25 ns access time eliminates wait states, enabling deterministic boot timing critical for real-time startup.

Test Equipment Configuration Memory

Avionics Maintenance Interface ROM

Use Scenario: Automated test equipment stores calibration constants, test sequence definitions, and instrument configuration tables.

IC Role / Device Role / Timing Role: Read-only data storage accessed during self-test and setup phases.

Use Value: SOIC-28 footprint allows replacement without board redesign; UV-erase supports recalibration data updates between deployments.

Use Scenario: Ground-support avionics tools embed diagnostic routines and protocol translators in fixed ROM for aircraft subsystem verification.

IC Role / Device Role / Timing Role: Dedicated firmware module executing serial command parsing and hardware register initialization.

Use Value: Commercial temperature range (0 °C to +70 °C) meets hangar and lab environmental requirements without derating.

Equivalent & Alternatives

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

Alternative Part	Technical Difference	Application Difference	Selection Advice
AM27C256B-25DC	25 ns access time, same 32K×8 organization, but uses AMD's bipolar process; higher active current (200 mA)	Compatible in pinout and timing, but requires tighter thermal management due to higher power dissipation	Prefer where existing AMD-based toolchains or programmers already support AM27C256B
AT27C256R-25JC	25 ns access time, 5 V-only operation (no V_PP pin), uses Atmel's CMOS process; standby current <10 µA	Eliminates need for high-voltage programming supply, but requires UV-erasable windowless package and different programming algorithm	Choose for lower-power systems where reprogramming frequency is low and UV exposure is controlled

Compared with AM27C256B-25DC and AT27C256R-25JC, the 27C256-25/SO277 offers balanced power-speed trade-off, proven UV-erase reliability, and broad programmer compatibility-making it optimal for long-lifecycle industrial upgrades where consistency matters more than ultra-low standby current or bipolar speed margins.

Availability

27C256-25/SO277 is available at Aetrix Electronics and suitable for industrial PLC firmware storage, legacy microcontroller boot ROM, and test equipment configuration memory requiring stable component supply over extended production lifecycles.

Supply support for 27C256-25/SO277 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 company specializing in microcontrollers, analog devices, and legacy-compatible memory solutions.

The 27C256-25/SO277 belongs to Microchip's classic EPROM product line, designed specifically for drop-in replacement of obsolete 27256 devices in maintenance, repair, and industrial retrofit applications.

FAQ

What is the programming voltage requirement for the 27C256-25/SO277?

The 27C256-25/SO277 requires 12.5 V applied to pin 1 (V_PP) during programming. This high voltage enables Fowler-Nordheim tunneling into the floating gate. Normal read operation uses only +5 V on V_CC; V_PP must be disconnected or held at 0 V outside programming mode. The 27C256-25/SO277 datasheet specifies strict tolerance (±0.5 V) on V_PP to prevent oxide damage.

Does the 27C256-25/SO277 support byte-level programming?

No, the 27C256-25/SO277 does not support byte-level programming. It uses standard EPROM programming architecture requiring full 32K-byte pattern loading via address and data bus. Each byte is written sequentially using a 50 µs pulse per location. The 27C256-25/SO277 must be programmed in-system or with a dedicated EPROM writer supporting NMOS EPROM protocols and V_PP sequencing.

Can the 27C256-25/SO277 be used as a direct replacement for the 27256 family?

Yes, the 27C256-25/SO277 is functionally and pin-compatible with industry-standard 27256 EPROMs, including the Intel 27256 and Mostek MK27256. It matches the 28-pin DIP and SOIC footprints, identical pinout, and TTL/CMOS electrical interface. The 27C256-25/SO277 maintains the same 25 ns access time and UV-erase window specification, making it a validated drop-in solution for legacy board repairs.

What UV wavelength and exposure duration are required to erase the 27C256-25/SO277?

The 27C256-25/SO277 requires exposure to 253.7 nm ultraviolet light for a minimum of 20 minutes to fully erase all memory cells. Erasure efficiency depends on lamp intensity, distance, and quartz window clarity. Microchip specifies that incomplete erasure may cause read failures or bit errors. The 27C256-25/SO277 must be erased before reprogramming, and its quartz window must remain unobstructed during exposure.

Is the 27C256-25/SO277 compliant with RoHS or lead-free standards?

The 27C256-25/SO277 is not RoHS-compliant. It contains lead in the solderable matte tin finish and uses leaded glass in the quartz UV window. Microchip discontinued RoHS conversion for this part due to obsolescence status and lack of demand for lead-free variants. Customers requiring RoHS compliance should evaluate modern Flash alternatives or contact Aetrix Electronics for traceable legacy stock with full material declarations.

27C256-25/SO277 Specifications

Product attributes: Attribute value

Manufacturer:: Microchip Technology

Series:: -

Package/Case:: 28-SOIC (0.295", 7.50mm Width)

Packaging:: Bulk

Product Status:: Active

Programmable:: Not Verified

Memory Type:: Non-Volatile

Memory Format:: EPROM

Technology:: EPROM - OTP

Memory Size:: 256Kbit

Memory Organization:: 32K x 8

Memory Interface:: Parallel

Clock Frequency:: -

Write Cycle Time - Word, Page:: -

Access Time:: 250 ns

Voltage - Supply:: 4.5V ~ 5.5V

Operating Temperature:: 0°C ~ 70°C (TA)

Grade:: -

Qualification:: -

Mounting Type:: Surface Mount

Supplier Device Package:: 28-SOIC

27C256-25/SO277 FAQ

1.How can I place an order for 27C256-25/SO277 through Aetrix?

Please submit a Request for Quotation (RFQ) for 27C256-25/SO277 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 27C256-25/SO277 reliable?

The price and inventory of 27C256-25/SO277 are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for 27C256-25/SO277 is usually 5 days.

3.What payment methods are accepted for 27C256-25/SO277?

We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for 27C256-25/SO277 transactions.

Note: Certain payment methods may incur a processing fee.

4.How is shipping managed for 27C256-25/SO277?

27C256-25/SO277 orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.

Once your 27C256-25/SO277 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 27C256-25/SO277?

For technical support, including 27C256-25/SO277 datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your 27C256-25/SO277 requirements.

6.How does Aetrix verify that 27C256-25/SO277 is sourced from the original manufacturer or authorized distributors?

All 27C256-25/SO277 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 27C256-25/SO277 meets industry standards.

7.What is the process for return or replacement of 27C256-25/SO277?

All 27C256-25/SO277 units undergo pre-shipment inspection (PSI). If there is an issue with 27C256-25/SO277, 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 27C256-25/SO277 part is unused and in its original packaging.

Return procedure for 27C256-25/SO277:

1.Submit a request within 90 days.

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

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