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

STMicroelectronics M27C256B-12B1

Name: M27C256B-12B1
Brand: STMicroelectronics
SKU: M27C256B-12B1
Price: 2.40 USD
Availability: InStock
Rating: 5 (2 reviews)

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Part No.:: M27C256B-12B1

Manufacturer:: STMicroelectronics

Category:: Memory

Package:: 28-DIP (0.600", 15.24mm)

Datasheet:: M27C256B-12B1.pdf

Description:: IC EPROM 256KBIT PARALLEL 28DIP

Quantity:: RFQ Add To RFQ list

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Inventory:1,400

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Product details

Overview

M27C256B-12B1 from STMicroelectronics is a 256 Kbit (32K × 8) UV-erasable EPROM in PDIP28 package, operating at 5V ±10%, with 120 ns access time, 30 mA active current, and 100 µA standby current. It features dual-line control (E/G), electronic signature (20h/8Dh), and supports programming at 12.75 V for embedded microprocessor memory applications.

For engineers reviewing the M27C256B-12B1 datasheet, M27C256B-12B1 pinout, M27C256B-12B1 application, or M27C256B-12B1 equivalent, key selection criteria include UV erasability, TTL-compatible timing, two-line output enable architecture, and compatibility with legacy 8-bit bus systems requiring non-volatile program storage.

Technical Context

The M27C256B-12B1 implements a classic NMOS-derived EPROM architecture with separate Chip Enable (E) and Output Enable (G) inputs enabling low-power array deselection and bus contention avoidance. Its read mode requires both E and G asserted low to drive Q0–Q7 outputs, while standby mode activates at CMOS-high E (≥ VCC − 0.2 V), reducing ICC to 100 µA.

Programming uses 12.75 V ±0.25 V on VPP with 100 µs pulse width per word at VCC = 6.25 V ±0.25 V; verify occurs under same VPP but with VCC = 6 V or 4.2 V for margin testing. Electronic signature reads manufacturer code 20h and device code 8Dh via A9 = 11.5–12.5 V and A0 toggling.

Key Specifications

Parameter	Value and Actual Design Meaning
Memory Size	256 Kbit (32,768 × 8), directly maps to 8-bit data bus without multiplexing
Access Time	120 ns max - defines minimum CPU wait-state requirement for 8 MHz Z80/8085/6502 systems
VCC Supply	5 V ±10% - compatible with standard TTL logic rails; no separate logic supply needed
Standby Current	100 µA - enables low-power retention in battery-backed or intermittent operation modes
VPP Programming Voltage	12.75 V ±0.25 V - requires dedicated high-voltage generator; not derived from VCC
Electronic Signature	Manufacturer Code 20h / Device Code 8Dh - enables automatic algorithm selection in universal programmers
Operating Temp	−40 °C to 85 °C - validated for industrial-grade embedded controller environments

Pinout & Package

PDIP28 (Package Code B), 600-mil wide plastic dual in-line package with 0.1-inch lead pitch; 28-pin through-hole mounting compatible with legacy PCB layouts and socket-based development systems.

Pin/Terminal	Circuit Role	Design Meaning
A0–A14	Address Inputs	15-bit address bus (32K locations); A9 used as VID select for electronic signature
Q0–Q7	Data Outputs	8-bit bidirectional data bus during programming (data-in) and read (data-out)
E	Chip Enable	Primary device select; CMOS-high places device in 100 µA standby; TTL-low enables array
G	Output Enable	Secondary gate; controls Q0–Q7 output drivers independently of E; avoids bus contention
VPP	Programming Supply	12.75 V input required only during programming; must be applied after VCC and removed before VCC
VCC	Supply Voltage	5 V ±10% for read; 6.25 V ±0.25 V for programming - strict sequencing required
VSS	Ground	Reference return for all signals; decoupling capacitor (0.1 µF ceramic) required adjacent to pin
NC	No Connect	Pins 16 and 24 (PLCC variant) are unconnected; not bonded in PDIP28 configuration

Key Features

Feature	Design Value
Two-line output control (E + G)	Enables full bus isolation: deselected devices draw only 100 µA and present Hi-Z outputs
UV erasability (FDIP28W variant)	15–20 min exposure to 2537 Å UV lamp (12 mW/cm²) fully resets all bits to '1'
Electronic signature support	Reads 20h/8Dh codes via A9 high-voltage bias - eliminates manual device selection in automated programmers
PRESTO II programming algorithm	Guarantees cell margin without overprogramming; typical full-array write time: 3.5 seconds
Wide temperature range	Specified from −40 °C to +85 °C - suitable for industrial control panels and automotive ECUs

Applications

Industrial PLC Firmware Storage

Legacy Microcontroller Boot ROM

Use Scenario: Storing fixed ladder logic firmware in DIN-rail mounted programmable logic controllers with no field update requirement.

IC Role / Device Role / Timing Role: Non-volatile boot memory mapped to CPU address space; accessed during power-on reset sequence with 120 ns timing compliance.

Use Value: UV erasability allows factory reprogramming between production batches; PDIP28 enables socket-based firmware replacement without soldering.

Use Scenario: Providing immutable startup code for Z80- or 8051-based instrumentation systems deployed in remote monitoring stations.

IC Role / Device Role / Timing Role: Read-only memory executing from 0x0000–0x7FFF; timing-critical due to lack of wait-state generators in legacy CPUs.

Use Value: Dual E/G control prevents bus contention when multiple EPROMs share data lines; 100 µA standby draws negligible current from backup batteries.

Medical Device Calibration Tables

Avionics Panel Display Firmware

Use Scenario: Holding factory-calibrated sensor offset/gain coefficients in Class II medical analyzers where data integrity is critical and updates are rare.

IC Role / Device Role / Timing Role: Static lookup table accessed via indirect addressing; verified during pre-deployment QA using electronic signature.

Use Value: Electronic signature (20h/8Dh) confirms genuine STMicroelectronics silicon, satisfying traceability requirements in regulated environments.

Use Scenario: Storing display initialization sequences and font bitmaps in certified cockpit display units where firmware must remain unchanged for airworthiness.

IC Role / Device Role / Timing Role: Memory-mapped peripheral holding static graphics assets; accessed during cold start with deterministic 120 ns latency.

Use Value: Ceramic FDIP28W variant (UV-erasable) supports rework in certified repair stations; PDIP28 variant satisfies cost-sensitive production builds.

Equivalent & Alternatives

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

Alternative Part	Technical Difference	Application Difference	Selection Advice
AM27C256B-120	Same 256 Kbit × 8 organization, 120 ns access, 5 V supply; manufactured by Advanced Micro Devices; identical pinout and AC/DC specs	Validated in AMD-specific programmer ecosystems; minor differences in VPP tolerance (12.5 V ±0.5 V vs. ST's 12.75 V ±0.25 V)	Select when sourcing from AMD-dedicated distributors or when cross-programmer compatibility is confirmed
AT27C256B-12JC	Atmel version with identical 256 Kbit × 8, 120 ns, 5 V operation; same PDIP28 footprint; differs in programming voltage (12.5 V) and electronic signature codes (1Fh/8Dh)	Used in Atmel-designated industrial controllers; signature mismatch prevents auto-algorithm detection in ST-optimized programmers	Choose for Atmel-centric BOMs or where second-source qualification mandates Atmel qualification testing

Compared with AM27C256B-120 and AT27C256B-12JC, the M27C256B-12B1 offers tighter VPP regulation (±0.25 V), broader temperature grading (−40 °C to +85 °C vs. −40 °C to +70 °C for some variants), and ST-specific signature codes that ensure correct algorithm selection in ST-validated programming workflows.

Availability

M27C256B-12B1 is available at Aetrix Electronics and suitable for industrial PLC firmware storage, legacy microcontroller boot ROM, medical device calibration tables, and avionics panel display firmware requiring stable component supply across extended product lifecycles.

Supply support for M27C256B-12B1 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 management ICs with strong heritage in non-volatile memory design.

The M27C256B belongs to ST's legacy EPROM product line, engineered for reliability in mission-critical embedded systems where long-term data retention, UV field reprogrammability, and pin-level compatibility with 1980s–1990s microprocessor buses are essential.

FAQ

What is the maximum recommended UV erasure dose for M27C256B-12B1?

The minimum integrated UV dose is 15 W·sec/cm² at 2537 Å wavelength. Using a 12,000 µW/cm² lamp, erasure takes 15–20 minutes at 2.5 cm distance. Overexposure beyond 30 minutes risks oxide damage and parametric shift; opaque window labels prevent accidental erasure under fluorescent lighting.

Can M27C256B-12B1 operate with VCC = 5 V during programming?

No. Programming requires VCC = 6.25 V ±0.25 V and VPP = 12.75 V ±0.25 V applied in strict sequence: VCC must be stable before VPP, and VPP must be removed before VCC. Using 5 V for programming causes incomplete cell threshold shifts and verification failure.

Is the PDIP28 package of M27C256B-12B1 UV-erasable?

No. Only the FDIP28W (window ceramic) package supports UV erasure. The "B" suffix in M27C256B-12B1 denotes PDIP28 - an OTP (one-time programmable) variant. Erasure is physically impossible in plastic packages due to UV-blocking material.

How does the electronic signature mode function on M27C256B-12B1?

Apply 11.5–12.5 V to A9 while holding VCC = VPP = 5 V and all other address lines low. Toggle A0: Q7–Q0 output shows 20h (manufacturer code) when A0 = low, then 8Dh (device code) when A0 = high. This mode operates only at 25 °C ±5 °C and is used exclusively by programming equipment for auto-identification.

M27C256B-12B1 Specifications

Product attributes: Attribute value

Manufacturer:: STMicroelectronics

Series:: -

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

Packaging:: Tube

Product Status:: Obsolete

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:: 120 ns

Voltage - Supply:: 4.5V ~ 5.5V

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

Grade:: -

Qualification:: -

Mounting Type:: Through Hole

Supplier Device Package:: 28-PDIP

M27C256B-12B1 FAQ

1.How can I place an order for M27C256B-12B1 through Aetrix?

Please submit a Request for Quotation (RFQ) for M27C256B-12B1 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-12B1 reliable?

The price and inventory of M27C256B-12B1 are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for M27C256B-12B1 is usually 5 days.

3.What payment methods are accepted for M27C256B-12B1?

We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for M27C256B-12B1 transactions.

Note: Certain payment methods may incur a processing fee.

4.How is shipping managed for M27C256B-12B1?

M27C256B-12B1 orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.

Once your M27C256B-12B1 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-12B1?

For technical support, including M27C256B-12B1 datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your M27C256B-12B1 requirements.

6.How does Aetrix verify that M27C256B-12B1 is sourced from the original manufacturer or authorized distributors?

All M27C256B-12B1 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-12B1 meets industry standards.

7.What is the process for return or replacement of M27C256B-12B1?

All M27C256B-12B1 units undergo pre-shipment inspection (PSI). If there is an issue with M27C256B-12B1, 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-12B1 part is unused and in its original packaging.

Return procedure for M27C256B-12B1:

1.Submit a request within 90 days.

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

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