27C256T-15/SO - 256K 32Kx8 CMOS EPROM 150ns | Microchip Technology
Référence : 27C256T-15/SO ✗ Fin de vie| Qté | Prix unitaire | Total |
|---|---|---|
| 1 | $2.95 | $2,95 |
| 10 | $2.65 | $26,50 |
| 100 | $2.35 | $235,00 |
| 500 | $2.1 | $1 050,00 |
| 1 000 | $1.9 | $1 900,00 |
27C256T-15/SO Présentation
An EPROM (Erasable Programmable Read-Only Memory) is a non-volatile semiconductor memory that retains firmware or fixed data without power and can be erased with ultraviolet light when housed in a quartz-window package; the plastic SOIC variant is intended for one-time programming in production. Within the memory hierarchy it sits under Memory ICs, in the broader category of non-volatile parallel memory alongside EEPROM and flash, and remains common in legacy and industrial systems.
Key features include CMOS technology for low power consumption with 20 mA active current and 100 uA standby current, 150 ns maximum access time for asynchronous parallel interfacing, 3-state outputs, and Auto ID identification to aid automated programming equipment. Factory programming and auto-insertion-compatible plastic packages are supported.
The device uses CMOS process technology to achieve a low standby current of 100 uA, which is valuable in battery-backed or power-sensitive legacy designs. Access is fully asynchronous with /CE, /OE, and PGM control lines, and the 3-state outputs allow direct bus connection in microprocessor systems.
Typical applications include legacy firmware storage in industrial controllers, automotive ECUs and engine-management ROM sockets, telecommunications equipment, and retro-computing repair where a 27C256 socket must be populated with a surface-mount device.
Design consideration: since this is an EPROM, the programmed content cannot be electrically erased; verify firmware on a programmer before soldering, and respect the 4.5V to 5.5V VCC window and programming voltage requirements on VPP.
This page synthesizes distributor availability data, drop-in alternatives, and practical design notes not consolidated in the manufacturer datasheet. Pricing references are as of 2026-09-13.
Alternatives de remplacement direct pour 27C256T-15/SO — même boîtier, compatible broche à broche. Les références à boîtier différent nécessitant une retouche du PCB sont exclues.
Variantes de cette série
Modèles de la même série directement compatibles avec 27C256T-15/SO (même facteur de forme et même empreinte) — différant par Package, Memory Type, Mounting Type, Organization, Erase Method.
Outil de comparaison rapide — sélectionnez des références alternatives pour une comparaison côte à côte :
27C256-15/SO
✅ Remplacement direct📋 Alternative de référence (hors catalogue)
27C256T-15E/SO
✅ Remplacement direct📋 Alternative de référence (hors catalogue)
27C256T-15I/SO
✅ Remplacement direct📋 Alternative de référence (hors catalogue)
W27E257-15
✅ Remplacement direct📋 Alternative de référence (hors catalogue)
AT27C256
✅ Remplacement direct📋 Alternative de référence (hors catalogue)
27C256T-15/SO Spécifications
| Type de mémoire | CMOS EPROM (non-volatile) |
| Memory Organization | 32K x 8 (256 Kbit) |
| Total Density | 262,144 bits |
| Maximum Access Time | 150 ns |
| Supply Voltage (VCC) | 4.5 V to 5.5 V |
| Interface | Parallel, asynchronous |
| Type de sortie | 3-state outputs |
| Active Current | 20 mA |
| Standby Current | 100 uA |
| Technology | CMOS |
| Operation Mode | Asynchronous |
| Auto ID | Yes (automated programming identification) |
| Boîtier | 28-lead SOIC (SO), surface mount |
| Type de montage | Surface Mount |
Configuration des broches de 27C256T-15/SO
| Broche 1 | VPP — Programming supply voltage |
| Broche 2 | A12 — Address input 12 (MSB) |
| Broche 3 | A7 — Address input 7 |
| Broche 4 | A6 — Address input 6 |
| Broche 5 | A5 — Address input 5 |
| Broche 6 | A4 — Address input 4 |
| Broche 7 | A3 — Address input 3 |
| Broche 8 | A2 — Address input 2 |
| Broche 9 | A1 — Address input 1 |
| Broche 10 | A0 — Address input 0 (LSB) |
| Broche 11 | O0 — Data output 0 (LSB) |
| Broche 12 | O1 — Data output 1 |
| Broche 13 | O2 — Data output 2 |
| Broche 14 | GND — Ground |
| Broche 15 | O3 — Data output 3 |
| Broche 16 | O4 — Data output 4 |
| Broche 17 | O5 — Data output 5 |
| Broche 18 | O6 — Data output 6 |
| Broche 19 | O7 — Data output 7 (MSB) |
| Broche 20 | /CE — Chip enable (active low) |
| Broche 21 | A10 — Address input 10 |
| Broche 22 | /OE — Output enable (active low) |
| Broche 23 | A11 — Address input 11 |
| Broche 24 | A9 — Address input 9 |
| Broche 25 | A8 — Address input 8 |
| Broche 26 | A13 — Address input 13 |
| Broche 27 | PGM — Program enable (active low) |
| Broche 28 | VCC — Power supply, 4.5V to 5.5V |
Applications typiques
27C256T-15/SO convient pour 6 applications: Legacy Industrial Controller Firmware, Automotive ECU ROM Replacement, Retro-Computing and Arcade Board Repair, Telecommunications Equipment Firmware, Test and Measurement Instrument ROM, Embedded Security and Fixed-Code Storage.
Legacy Industrial Controller Firmware
The 27C256T-15/SO stores boot firmware and fixed lookup tables in legacy PLC and industrial controllers that still use 27C256 sockets. Its 150 ns access time is compatible with 8-bit and 16-bit microprocessor buses from the 1980s and 1990s, and the 100 uA CMOS standby current suits equipment that must retain code through power cycles without a battery. Because the 28-lead SOIC footprint matches the original design, failing through-hole or socketed parts can be replaced with a surface-mount device on an adapter or a matching SOIC footprint. Content programmed in production cannot be altered in the field, which is an advantage where firmware integrity and tamper-resistance are required, but demands rigorous pre-programming verification.
Recommandé
Automotive ECU ROM Replacement
Engine-control units of the 1990s era commonly used 27C256 EPROMs for fuel and ignition maps. The 27C256T-15/SO provides the same 32K x 8 organization and 150 ns access timing required by these ECUs, with 4.5V to 5.5V operation matching the automotive 5V regulator rail and 3-state outputs interfacing directly to the MCU bus. For repair and remapping work, choose the industrial (27C256T-15I/SO) or extended (27C256T-15E/SO) temperature grades when the underhood environment exceeds commercial limits. As a one-time-programmable device, each calibration revision requires a new part, so electrically erasable substitutes such as the W27E257-15 are popular during development, with the OTP EPROM used for the final production fit.
Recommandé
Retro-Computing and Arcade Board Repair
Vintage PC, console, and arcade motherboards rely on 27C256 EPROMs for BIOS and game code, and replacement parts are the primary repair path as originals fail or are lost. The 27C256T-15/SO matches the original 150 ns speed grade, and the minuszerodegrees replacement guide confirms that 150 ns devices are suitable for IBM 5155/5160/5162/5170 motherboards, where access time acts as a maximum rating. The 28-lead SOIC package suits boards converted to surface mount or fitted with SOIC sockets. Programmers with Auto ID support automatically identify the device, simplifying batch programming of replacement ROMs for collectors and repair shops restoring large quantities of boards.
Recommandé
Telecommunications Equipment Firmware
Older telecom line cards, modems, and PBX modules used 27C256 EPROMs for code storage, and field-service organizations still need replacements to keep installed bases running. The device's asynchronous parallel interface, 3-state outputs, and 20 mA active current fit directly into these 5V bus-based designs without glue-logic changes. The SOIC surface-mount package supports automated rework on modern assembly lines repairing surface-mount cards, and tape-and-reel packaging (the T suffix) supports pick-and-place placement during volume refurbishment. Because telecom deployments often run for decades, stocking a lifecycle-stable replacement such as this EOL-class EPROM or its pin-compatible industrial variant protects long-term serviceability of the installed base.
Recommandé
Test and Measurement Instrument ROM
Older oscilloscopes, logic analyzers, and bench instruments from the 1990s store self-test and operating firmware in 27C256 EPROMs, and instrument repair often requires replacement parts with exact timing. The 27C256T-15/SO delivers the 150 ns maximum access time expected by these designs, and its 100 uA standby current keeps battery-backed memory subsystems within budget. In repair workflows, the instrument firmware image is recovered from a donor unit or archived dump, programmed into the EPROM with verification, and soldered or socketed in place of the failed device. Since the plastic SOIC cannot be erased, service centers typically program spares in batches and store them as serialized inventory for field swap-outs.
Recommandé
Embedded Security and Fixed-Code Storage
Applications that must store fixed identifiers, encryption keys, or boot constants benefit from the inherently immutable nature of a programmed EPROM: unlike flash or EEPROM, a soldered-in 27C256T-15/SO cannot be electrically rewritten, providing a simple hardware-level tamper barrier without extra security circuitry. The 32K x 8 capacity holds code plus fixed tables comfortably, the 4.5V to 5.5V supply matches standard industrial 5V rails, and the 150 ns access time meets typical 8-bit MCU bus timing. Designers should treat program content as permanent - any revision means a new programmed device - and should protect pin 1 (VPP) and the /PGM line on the PCB so that in-system programming attempts are physically prevented.
Recommandé
Récapitulatif des produits recommandés
Données de référence d'ingénierie pour 27C256T-15/SO — comparaison, recommandations de conception et informations de conformité.
Guide de sélection
Comparaison avec les alternatives
| Paramètre | Ce produit | 27C256-15/SO | 27C256T-15I/SO | W27E257-15 | AT27C256 |
|---|---|---|---|---|---|
| Package | 28-lead SOIC | 28-lead SOIC - same | 28-lead SOIC - same | 28-pin (SOIC/DIP) - same footprint | 28-pin (SOIC/DIP/PLCC) - SOIC same footprint |
| Brand | Microchip Technology (Fairchild legacy listing) | Microchip Technology | Microchip Technology | Winbond | Microchip Technology (Atmel) |
| Memory Organization | 32K x 8 (256 Kbit) | 32K x 8 | 32K x 8 | 32K x 8 | 32K x 8 |
| Maximum Access Time | 150 ns | 150 ns | 150 ns | 150 ns | Faster grades available (55-150 ns) |
| Supply Voltage | 4.5 V to 5.5 V | 4.5 V to 5.5 V | 4.5 V to 5.5 V | 4.5 V to 5.5 V | 4.5 V to 5.5 V |
| Erase Method | UV erase / OTP in plastic SOIC | UV erase / OTP in plastic SOIC | UV erase / OTP in plastic SOIC | Electrical erase (EEPROM) | OTP or windowed UV erase |
| Lifecycle Status | EOL (secondary market) | EOL (secondary market) | EOL (secondary market) | EOL (secondary market) | EOL (secondary market) |
Principaux différenciateurs
- Surface-mount 28-lead SOIC packaging for legacy sockets (vs 27C256-15/SO)
- Standard commercial temperature grade at lowest cost (vs 27C256T-15I/SO)
- Immutable UV/OTP EPROM behavior versus electrically erasable substitutes (vs W27E257-15)
- Exact original speed grade match (vs AT27C256)
Notes de conception
The 27C256T-15/SO in a plastic SOIC package is one-time programmable - there is no quartz window for UV erasure. Program and fully verify the firmware image in an external programmer (which can use Auto ID to identify the device) BEFORE assembly; a single bit error after reflow means scrapping the board or hot-air rework. Keep pin 1 (VPP) and pin 27 (PGM) routed to non-user-accessible points in security-sensitive designs so in-system programming is impossible.
Connect every VCC (pin 28) and GND (pin 14) with a 0.1 uF ceramic decoupling capacitor placed within a few millimeters of the package. Tie unused control lines properly: /CE (pin 20) and /OE (pin 22) must be actively driven or pulled up; leaving them floating can place outputs in undefined high-impedance states or increase active current beyond the 20 mA datasheet figure. Keep address lines short and equalized where bus timing approaches the 150 ns access budget.
The 150 ns maximum access time is a worst-case figure; the CPU address-to-data setup must satisfy t_ACC plus output-enable delays. When retrofitting this part into designs that originally used a faster grade, verify the timing margin: per the minuszerodegrees replacement guide, access time is a maximum rating, so a faster 27C256 always works where a 150 ns part was designed - but a 150 ns part in a faster socket is not guaranteed. If in doubt, qualify the faster 27C256 variants as second sources.
Informations de conformité
This is a legacy EOL part; RoHS status is not clearly stated in verified distributor data (some broker listings reference RoHS stock). Obtain a certificate of conformance from the seller if compliance is mandatory.
