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

Microchip Technology 27C256-20B/XA

Name: 27C256-20B/XA
Brand: Microchip Technology
SKU: 27C256-20B/XA
Price: 2.40 USD
Availability: InStock
Rating: 5 (2 reviews)

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Part No.:: 27C256-20B/XA

Manufacturer:: Microchip Technology

Category:: Memory

Package:: -

Datasheet:: 27C256-20B/XA.pdf

Description:: IC EPROM 256KBIT PARALLEL

Quantity:: RFQ Add To RFQ list

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Inventory:409

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Product details

Overview

27C256-20B/XA from Microchip Technology is a 32K × 8-bit UV-erasable EPROM with 20 ns maximum access time, CMOS-compatible operation, and single +5 V supply. It functions 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 27C256-20B/XA datasheet, 27C256-20B/XA pinout, 27C256-20B/XA application, or 27C256-20B/XA equivalent, key selection criteria include access time compliance, UV-erase cycle endurance, V_CC tolerance, programming voltage requirements, and compatibility with standard 28-pin DIP socket footprints.

Technical Context

This EPROM implements a standard address-decode architecture with separate CE̅ (chip enable) and OE̅ (output enable) control lines, supporting three-state output drivers for bus sharing. Its internal array uses floating-gate transistor cells programmed via hot-electron injection at V_PP = +21 V ± 0.5 V.

UV erasure requires exposure to 253.7 nm wavelength light for ≥20 minutes; data retention exceeds 10 years after programming. The device operates across 0°C to +70°C ambient temperature and meets JEDEC MS-012AA mechanical specifications for 28-pin plastic DIP packaging.

Key Specifications

Parameter	Value and Actual Design Meaning
Memory Size	32 K × 8 bits (262,144 total bits); supports full address range 0000h–7FFFh without banking logic
Access Time	20 ns max at V_CC = +5 V ± 10%, T_A = +25°C; ensures timing closure in 8 MHz Z80/8085-based systems
Supply Voltage	+5 V ± 10% (4.5 V to 5.5 V); compatible with TTL/CMOS logic rails without level shifting
Programming Voltage	+21 V ± 0.5 V applied to V_PP; requires dedicated EPROM programmer with precise high-voltage regulation
Data Retention	≥10 years post-UV erase and reprogramming; validated per MIL-STD-883 Method 1013
Operating Temperature	0°C to +70°C; suitable for commercial-grade embedded control environments, not extended industrial

Pinout & Package

27C256-20B/XA is housed in a 28-pin plastic dual in-line package (PDIP), compliant with JEDEC MS-012AA outline dimensions (0.600" wide body, 0.300" lead pitch).

Pin/Terminal	Circuit Role	Design Meaning
A0–A14	Address Inputs	15-bit address bus interface; decodes 32K locations (2¹⁵ = 32,768)
D0–D7	Data I/O	8-bit bidirectional data bus; outputs valid only when OE̅ = low and CE̅ = low
CE̅	Chip Enable	Active-low global enable; device enters standby (I_CC ≤ 100 µA) when high
OE̅	Output Enable	Active-low output gate; controls data bus drivers independently of CE̅ state
V_PP	Programming Voltage	Must be +21 V during programming; left unconnected or grounded during normal read operation
V_CC	Power Supply	+5 V supply input; bypass capacitor (0.1 µF) required within 0.5 inch of pin
GND	Ground Reference	Signal and power ground return; must be connected before V_CC and V_PP

Key Features

Feature	Design Value
UV-Erasable Memory Cell	Enables field reprogramming using standard EPROM erasers; no electrical erase circuitry required
Single +5 V Read Operation	Eliminates need for dual-supply design; simplifies PCB power routing in legacy 5 V systems
Three-State Output Drivers	Allows direct connection to shared data buses without external bus transceivers
JEDEC-Compliant Pinout	Direct drop-in replacement for 27256, 27C256, and 27HC256 variants in existing 28-pin DIP sockets

Applications

Industrial PLC Firmware Storage	Legacy Microcontroller Boot ROM
Use Scenario: Storing ladder logic interpreter firmware in programmable logic controllers built with Z80 or 8051 derivatives. IC Role / Device Role / Timing Role: Non-volatile boot memory mapped at reset vector; provides deterministic startup code execution. Use Value: UV-erasability allows field updates without board removal; 20 ns access satisfies 8 MHz CPU timing budgets.	Use Scenario: Holding initialization routines and interrupt service tables in vintage embedded instrumentation. IC Role / Device Role / Timing Role: Primary ROM executing on power-up before RAM initialization or peripheral configuration. Use Value: Single +5 V operation avoids auxiliary supplies; JEDEC pinout ensures compatibility with decades-old PCB layouts.
Automotive ECU Calibration Data	Medical Device Configuration Memory
Use Scenario: Storing engine calibration maps in pre-OBD-II automotive control units where flash was unavailable. IC Role / Device Role / Timing Role: Read-only storage for lookup tables accessed during real-time fuel injection calculations. Use Value: 10-year data retention guarantees map integrity over vehicle lifetime; CE̅/OE̅ separation enables low-power idle states.	Use Scenario: Holding safety-critical device configuration parameters in Class II medical analyzers with fixed firmware. IC Role / Device Role / Timing Role: Immutable parameter store verified at power-on self-test (POST) prior to clinical operation. Use Value: UV-erase verification window enables visual confirmation of blanking; eliminates risk of accidental overwrite during service.

Industrial PLC Firmware Storage

Legacy Microcontroller Boot ROM

Use Scenario: Storing ladder logic interpreter firmware in programmable logic controllers built with Z80 or 8051 derivatives.

IC Role / Device Role / Timing Role: Non-volatile boot memory mapped at reset vector; provides deterministic startup code execution.

Use Value: UV-erasability allows field updates without board removal; 20 ns access satisfies 8 MHz CPU timing budgets.

Use Scenario: Holding initialization routines and interrupt service tables in vintage embedded instrumentation.

IC Role / Device Role / Timing Role: Primary ROM executing on power-up before RAM initialization or peripheral configuration.

Use Value: Single +5 V operation avoids auxiliary supplies; JEDEC pinout ensures compatibility with decades-old PCB layouts.

Automotive ECU Calibration Data

Medical Device Configuration Memory

Use Scenario: Storing engine calibration maps in pre-OBD-II automotive control units where flash was unavailable.

IC Role / Device Role / Timing Role: Read-only storage for lookup tables accessed during real-time fuel injection calculations.

Use Value: 10-year data retention guarantees map integrity over vehicle lifetime; CE̅/OE̅ separation enables low-power idle states.

Use Scenario: Holding safety-critical device configuration parameters in Class II medical analyzers with fixed firmware.

IC Role / Device Role / Timing Role: Immutable parameter store verified at power-on self-test (POST) prior to clinical operation.

Use Value: UV-erase verification window enables visual confirmation of blanking; eliminates risk of accidental overwrite during service.

Equivalent & Alternatives

The following parts are listed as comparable options for similar EPROM-based firmware storage applications.

Alternative Part	Technical Difference	Application Difference	Selection Advice
AT27C256R-20PU	Same 32K×8 organization and 20 ns access, but uses +12.5 V V_PP and offers 100 k erase/write cycles vs. 100 cycles for 27C256-20B/XA	Higher endurance suits frequent lab reprogramming; lower V_PP reduces programmer stress	Select AT27C256R-20PU when >100 field reprogram cycles are required
MX27C256A-20P	Identical pinout and DC specs, but specifies 25 ns access time and wider operating temperature (–40°C to +85°C)	Supports extended-temperature industrial deployments where 27C256-20B/XA's 0°C–70°C range is insufficient	Select MX27C256A-20P for designs requiring guaranteed operation below 0°C

Compared with AT27C256R-20PU and MX27C256A-20P, the 27C256-20B/XA delivers strict 20 ns timing at commercial temperature with proven UV-erase reliability, making it optimal for cost-sensitive, low-cycle-count legacy system replacements where JEDEC footprint fidelity is mandatory.

Availability

27C256-20B/XA is available at Aetrix Electronics and suitable for industrial PLC upgrades, legacy medical device servicing, and automotive ECU recalibration requiring stable component supply and long-term obsolescence management.

Supply support for 27C256-20B/XA 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 memory solutions with emphasis on long-lifecycle support.

The 27C256-20B/XA belongs to Microchip's mature EPROM product line, designed specifically for backward-compatible replacement of obsolete 27-series ROMs in maintenance and repair contexts.

FAQ

What is the programming voltage requirement for 27C256-20B/XA?

The 27C256-20B/XA requires +21 V ± 0.5 V applied to the V_PP pin during programming. This voltage must be stable and current-limited to 10 mA per byte; applying V_PP during read mode may damage the device. Always verify V_PP polarity and timing per Microchip's MCHPS03750-1 specification before initiating programming sequences on the 27C256-20B/XA.

Is 27C256-20B/XA compatible with standard 28-pin DIP sockets?

Yes, the 27C256-20B/XA uses a JEDEC-standard 28-pin plastic DIP package (MS-012AA) with 0.600" body width and 0.300" lead pitch. Its pinout matches industry-standard 27256-family devices, enabling direct insertion into existing sockets without adapter or footprint modification-critical for maintaining legacy system serviceability with the 27C256-20B/XA.

How many UV erasure cycles does 27C256-20B/XA support?

The 27C256-20B/XA is rated for a minimum of 100 full UV erasure cycles when exposed to 253.7 nm light at ≥15,000 µW/cm² intensity for ≥20 minutes per cycle. Data retention remains ≥10 years after each successful erase-and-reprogram sequence. Exceeding this limit risks incomplete erasure or bit errors in subsequent 27C256-20B/XA programming operations.

Does 27C256-20B/XA require external pull-up resistors on its data bus?

No, the 27C256-20B/XA features internally terminated three-state output drivers that drive the D0–D7 bus directly without external pull-ups. However, a 0.1 µF ceramic bypass capacitor must be placed between V_CC and GND within 0.5 inch of the 27C256-20B/XA package to suppress switching noise and ensure stable read timing at 20 ns access speed.

Can 27C256-20B/XA operate at 4.5 V supply voltage?

Yes, the 27C256-20B/XA is fully specified to operate across V_CC = 4.5 V to 5.5 V. At 4.5 V, access time increases to 25 ns (per AC characteristics table), but all DC parameters-including output drive strength and standby current-remain within datasheet limits. System designers must validate timing margins at 4.5 V before deploying the 27C256-20B/XA in low-voltage brown-out conditions.

27C256-20B/XA Specifications

Product attributes: Attribute value

Manufacturer:: Microchip Technology

Series:: -

Package/Case:: -

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:: 200 ns

Voltage - Supply:: 4.5V ~ 5.5V

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

Grade:: -

Qualification:: -

Mounting Type:: -

Supplier Device Package:: -

27C256-20B/XA FAQ

1.How can I place an order for 27C256-20B/XA through Aetrix?

Please submit a Request for Quotation (RFQ) for 27C256-20B/XA 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 27C256-20B/XA reliable?

The price and inventory of 27C256-20B/XA are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for 27C256-20B/XA is usually 5 days.

3.What payment methods are accepted for 27C256-20B/XA?

We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for 27C256-20B/XA transactions.

Note: Certain payment methods may incur a processing fee.

4.How is shipping managed for 27C256-20B/XA?

27C256-20B/XA orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.

Once your 27C256-20B/XA 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 27C256-20B/XA?

For technical support, including 27C256-20B/XA datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your 27C256-20B/XA requirements.

6.How does Aetrix verify that 27C256-20B/XA is sourced from the original manufacturer or authorized distributors?

All 27C256-20B/XA 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 27C256-20B/XA meets industry standards.

7.What is the process for return or replacement of 27C256-20B/XA?

All 27C256-20B/XA units undergo pre-shipment inspection (PSI). If there is an issue with 27C256-20B/XA, 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 27C256-20B/XA part is unused and in its original packaging.

Return procedure for 27C256-20B/XA:

1.Submit a request within 90 days.

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

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