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

STMicroelectronics M27C256B-12F6

Name: M27C256B-12F6
Brand: STMicroelectronics
SKU: M27C256B-12F6
Price: 2.40 USD
Availability: InStock
Rating: 5 (2 reviews)

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Part No.:: M27C256B-12F6

Manufacturer:: STMicroelectronics

Category:: Memory

Package:: 28-CDIP (0.600", 15.24mm) Window

Datasheet:: M27C256B-12F6.pdf

Description:: IC EPROM 256KBIT PARALLEL 28CDIP

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Product details

Overview

M27C256B-12F6 from STMicroelectronics is a 256 Kbit (32K × 8) UV-erasable EPROM in FDIP28W ceramic window package, operating at 5V ±10%, with 120 ns access time, 30 mA active current, and 100 µA standby current. It serves as non-volatile program storage in legacy microprocessor systems requiring field-erasable firmware, such as industrial PLCs, telecom line cards, and embedded boot memory.

For engineers reviewing the M27C256B-12F6 datasheet, M27C256B-12F6 pinout, M27C256B-12F6 application, or M27C256B-12F6 equivalent, key selection criteria include UV erasure capability, dual-line output control (E/G), electronic signature support (20h/8Dh), and compatibility with TTL-level address/data buses in 8-bit microarchitectures.

Technical Context

The M27C256B-12F6 implements a two-control-line architecture (Chip Enable E and Output Enable G) to minimize bus contention and power dissipation in multi-device memory arrays. Its read mode requires simultaneous VCC = 5V ±10% and stable TTL-level inputs, with timing referenced to 1.5V for high-speed AC testing (30 pF load).

Programming operates at elevated voltages: VPP = 12.75V ±0.25V and VCC = 6.25V ±0.25V, using 100 µs pulses per word and PRESTO II margin-verified algorithm. Electronic signature mode activates via 12V on A9 (11.5–12.5V) with VCC = VPP = 5V to output manufacturer code 20h and device code 8Dh on Q7–Q0.

Key Specifications

Parameter	Value and Actual Design Meaning
Memory Size	256 Kbit (32,768 × 8 bits) - supports full 16-bit address space with byte-wide data interface
Access Time	120 ns - defines maximum clock rate for synchronous read cycles in 8-bit bus systems
Supply Voltage	5V ±10% in read mode - compatible with standard TTL/CMOS logic rails without regulation
Active Current	30 mA at 5 MHz - determines decoupling capacitor sizing (0.1 µF ceramic + 4.7 µF bulk per 8 devices)
Standby Current	100 µA - enables low-power retention during CPU wait states or idle periods
Programming Voltage	VPP = 12.75V ±0.25V - requires dedicated programming supply; not compatible with standard 5V system rails
Erasure Method	UV light (2537 Å, ≥15 W·s/cm²) - mandates FDIP28W window package; irreversible for OTP variants

Pinout & Package

FDIP28W (28-pin ceramic frit-seal DIP with UV-transparent window) - mechanical dimensions per STMicroelectronics spec: 36.5–37.3 mm length, 15.2 mm width, 4.57 mm height, 2.54 mm lead pitch.

Pin/Terminal	Circuit Role	Design Meaning
A0–A14	Address Inputs	15-bit address bus supporting 32K-word addressing; A9 used for electronic signature voltage injection
Q0–Q7	Data Outputs	Bi-directional I/O pins used for parallel data input during programming and output during read
E	Chip Enable	Primary device select; CMOS-high places device in 100 µA standby; TTL-low enables memory array
G	Output Enable	Secondary output gate; independent of E, prevents bus contention when shared across multiple EPROMs
VPP	Programming Supply	12.75V input required only during programming/verify; must be applied simultaneously with or after VCC
VCC	Power Supply	5V ±10% for read; 6.25V ±0.25V for programming - strict sequencing required to avoid latch-up
VSS	Ground	Reference for all I/O and internal logic; separate decoupling path required per device
NC	No Connect	Internally unconnected pins (e.g., PLCC32 pin 17); must remain floating or grounded per layout rules
DU	Don't Use	Reserved pins (e.g., PLCC32 pin 32); no internal connection; avoid routing or termination

Key Features

Feature	Design Value
Dual-line output control (E + G)	Eliminates bus contention in multi-chip memory banks by enabling independent chip selection and output gating
Electronic signature (20h/8Dh)	Enables automatic device identification in programming hardware, preventing algorithm mismatches during firmware burn-in
PRESTO II programming algorithm	Guarantees cell margin verification per byte without over-programming pulses, reducing write failure risk
UV erasure compatibility	FDIP28W package allows full bit-pattern reset using 2537 Å UV light (15–20 min exposure at 12,000 µW/cm²)
TTL-compatible I/O levels	Accepts standard 0.8V/2.0V logic thresholds and drives 2.1mA loads at 0.4V VOL, simplifying integration with 8080/Z80/6502 systems

Applications

Industrial PLC Firmware Storage

Telecom Line Card Boot Memory

Use Scenario: Storing ladder logic firmware in programmable logic controllers deployed in factory automation environments with ambient temperatures up to 85°C.

IC Role / Device Role / Timing Role: Non-volatile boot ROM providing instruction fetch during cold start; accessed via 8-bit data bus with 120 ns tACC timing constraint.

Use Value: UV erasability enables field firmware updates without board replacement; FDIP28W window allows localized reprogramming in situ.

Use Scenario: Holding initialization code and protocol stacks in T1/E1 line interface cards operating in temperature-controlled telecom central offices.

IC Role / Device Role / Timing Role: Primary boot memory mapped to CPU address space; selected via decoded E signal while G synchronizes with system READ strobe.

Use Value: Dual E/G control ensures zero bus contention during hot-swap events; 100 µA standby current reduces thermal load in dense card cages.

Legacy Microcomputer BIOS

Military Avionics Configuration Data

Use Scenario: Providing BIOS firmware for 8088/8086-based embedded controllers in test equipment and lab instruments.

IC Role / Device Role / Timing Role: Read-only memory mapped at fixed segment; timing-critical for first instruction fetch after reset (tAVQV = 120 ns).

Use Value: Electronic signature (20h/8Dh) validates correct device insertion before programming, preventing bricking during field upgrades.

Use Scenario: Storing flight-critical configuration tables in avionics subsystems qualified to –40°C to +125°C operating range.

IC Role / Device Role / Timing Role: Radiation-tolerant non-volatile storage; accessed during pre-flight self-test with guaranteed 120 ns access under worst-case voltage/temperature corners.

Use Value: Ceramic FDIP28W package provides hermetic sealing and UV erasure traceability for DO-254 compliance documentation.

Equivalent & Alternatives

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

Alternative Part	Technical Difference	Application Difference	Selection Advice
AM27C256B-120	Same 256K×8 organization, 120 ns access, but uses AMD's proprietary programming algorithm and signature codes (01h/8Dh)	Requires AMD-specific programmer firmware; not interchangeable in ST-validated production lines	Select only if existing toolchain supports AMD signature and timing margins
MX27C256-12PC	120 ns access, PDIP28 package, but lacks electronic signature and UV erasure (OTP-only variant)	Suitable for one-time firmware deployment only; no field reprogrammability or device ID verification	Choose for cost-sensitive, non-upgradable applications where window package is unnecessary

Compared with M27C256B-12F6, AM27C256B-120 offers identical timing but requires vendor-specific programming infrastructure, while MX27C256-12PC sacrifices UV erasure and signature for lower cost and simpler handling - neither matches the ST device's combination of field reprogrammability, automated ID validation, and ceramic reliability.

Availability

M27C256B-12F6 is available at Aetrix Electronics and suitable for industrial PLC firmware updates, telecom line card boot memory, and legacy microcomputer BIOS applications requiring stable component supply across extended product lifecycles.

Supply support for M27C256B-12F6 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

STMicroelectronics is a global semiconductor leader headquartered in Geneva, Switzerland, specializing in automotive, industrial, and power discrete solutions with vertical manufacturing capabilities.

The M27C256B belongs to ST's legacy EPROM product line, designed specifically for microprocessor-based systems requiring field-erasable, pin-compatible non-volatile memory with TTL interface compatibility and long-term data retention.

FAQ

What UV wavelength and exposure dose are required to fully erase M27C256B-12F6?

Full erasure requires short-wave ultraviolet light at 2537 Å wavelength with a minimum integrated dose of 15 W·s/cm². Using a 12,000 µW/cm² lamp, the recommended exposure time is 15–20 minutes at 2.5 cm distance. Room fluorescent lighting may cause partial erasure over years; direct sunlight can erase in ~1 week.

Can M27C256B-12F6 operate with VCC = 5V ±5% instead of ±10%?

Yes - the device supports both tolerances. The ±5% option (denoted by 'X' in ordering code) guarantees tighter AC timing parameters (e.g., 120 ns max tACC) across full temperature range, while ±10% allows broader supply variation at same speed grade. DC characteristics remain valid in both cases per Table 7.

Why does M27C256B-12F6 require separate VCC and VPP supplies during programming?

VCC is set to 6.25V ±0.25V to bias internal logic and sense amplifiers, while VPP = 12.75V ±0.25V provides the high-field voltage needed to inject charge into floating gates. Simultaneous application prevents latch-up; VPP must never be applied without VCC present, as specified in Tables 9 and 10.

Is the FDIP28W package RoHS-compliant?

No - the FDIP28W package contains leaded solder seals and ceramic materials not compliant with RoHS Directive 2011/65/EU. STMicroelectronics discontinued RoHS-compliant equivalents for this part number; modern replacements (e.g., M27C256B-12F6TR) retain the same package and composition.

M27C256B-12F6 Specifications

Product attributes: Attribute value

Manufacturer:: STMicroelectronics

Series:: -

Package/Case:: 28-CDIP (0.600", 15.24mm) Window

Packaging:: Tube

Product Status:: Obsolete

Programmable:: Not Verified

Memory Type:: Non-Volatile

Memory Format:: EPROM

Technology:: EPROM - UV

Memory Size:: 256Kbit

Memory Organization:: 32K x 8

Memory Interface:: Parallel

Clock Frequency:: -

Write Cycle Time - Word, Page:: -

Access Time:: 120 ns

Voltage - Supply:: 4.5V ~ 5.5V

Operating Temperature:: -40°C ~ 85°C (TA)

Grade:: -

Qualification:: -

Mounting Type:: Through Hole

Supplier Device Package:: 28-CDIP Frit Seal with Window

M27C256B-12F6 FAQ

1.How can I place an order for M27C256B-12F6 through Aetrix?

Please submit a Request for Quotation (RFQ) for M27C256B-12F6 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 M27C256B-12F6 reliable?

The price and inventory of M27C256B-12F6 are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for M27C256B-12F6 is usually 5 days.

3.What payment methods are accepted for M27C256B-12F6?

We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for M27C256B-12F6 transactions.

Note: Certain payment methods may incur a processing fee.

4.How is shipping managed for M27C256B-12F6?

M27C256B-12F6 orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.

Once your M27C256B-12F6 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 M27C256B-12F6?

For technical support, including M27C256B-12F6 datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your M27C256B-12F6 requirements.

6.How does Aetrix verify that M27C256B-12F6 is sourced from the original manufacturer or authorized distributors?

All M27C256B-12F6 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 M27C256B-12F6 meets industry standards.

7.What is the process for return or replacement of M27C256B-12F6?

All M27C256B-12F6 units undergo pre-shipment inspection (PSI). If there is an issue with M27C256B-12F6, 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 M27C256B-12F6 part is unused and in its original packaging.

Return procedure for M27C256B-12F6:

1.Submit a request within 90 days.

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

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