27C256A-12 - 256Kbit CMOS EPROM 32Kx8 120ns | NEC
Référence : 27C256A-12 ✗ Fin de vie| Qté | Prix unitaire | Total |
|---|---|---|
| 1 | $3.95 | $3,95 |
| 10 | $3.56 | $35,60 |
| 100 | $3.16 | $316,00 |
| 500 | $2.84 | $1 420,00 |
| 1 000 | $2.52 | $2 520,00 |
27C256A-12 Présentation
An EPROM is a non-volatile memory type in the broader memory hierarchy of semiconductor storage: memory IC -> read-only memory -> EPROM -> UV-erasable EPROM. Data is written electrically by a programming voltage (VPP) and erased in bulk by exposure to ultraviolet light through a quartz window, distinguishing it from electrically erasable EEPROM and flash memory.
Key features of the 27C256A include the fast 120 ns access time that supports zero-wait-state operation with 8- and 16-bit microprocessors, low CMOS standby power consumption, a single 5 V supply for read operation, and standard JEDEC-compatible 28-pin pinouts that enable drop-in substitution across multiple 27C256 vendors.
The device uses a CMOS cell architecture to reduce active and standby current dramatically compared with earlier NMOS 27256 parts, while preserving the industry-standard 27C256 timing model with address setup, chip enable, and output enable access specifications.
Typical applications include embedded firmware storage for 8-bit microcontrollers and microprocessors, industrial control equipment, telecommunications boards, legacy arcade and test equipment, and bios/boot code storage in older PC designs.
When designing with the 27C256A-12, verify the programming algorithm and VPP level against the specific manufacturer datasheet, since programming specifications vary between NEC, NXP/Philips, and Fujitsu versions even when pin-compatible.
This page synthesizes distributor availability, drop-in alternatives, and practical retrofit design notes not found in a single manufacturer datasheet, making it a unique resource for maintaining legacy EPROM-based systems.
Alternatives de remplacement direct pour 27C256A-12 — 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 27C256A-12 (même facteur de forme et même empreinte) — différant par Package, Memory Type, Organization, Erase Method, Mounting Type.
Outil de comparaison rapide — sélectionnez des références alternatives pour une comparaison côte à côte :
27C256L-20R
✅ Remplacement direct✓ En stock
$1.85 / unité
Voir la fiche technique →27C256T-15/SO
✅ Remplacement direct✓ En stock
$1.9 / unité
Voir la fiche technique →27C256A12A
✅ Remplacement direct📋 Alternative de référence (hors catalogue)
27C512-20
✅ Remplacement direct ⚠️ Spécifications non vérifiées✓ En stock
$4.1 / unité
Voir la fiche technique →27C512-10
✅ Remplacement direct✓ En stock
$2.7 / unité
Voir la fiche technique →27C256A-12 Valeurs maximales et caractéristiques électriques
| Type de mémoire | UV EPROM |
| Technology | CMOS |
| Taille de mémoire | 256 Kbit (32K x 8) |
| Organisation de la mémoire | 32K x 8 |
| Access Time | 120 ns |
| Supply Voltage (VCC) | 5 V |
| Interface | Parallel |
| Température de fonctionnement | 0C to +70C (commercial) |
| Boîtier | 28-pin DIP |
| Type de montage | Through Hole |
| Erase Method | Ultraviolet light |
| Statut RoHS | unknown |
| Statut du cycle de vie | Obsolete (legacy product) |
Configuration des broches de 27C256A-12
| Broche 1 | VPP — Programming supply voltage / program enable |
| Broche 2 | A12 — Address input |
| Broche 3 | A7 — Address input |
| Broche 4 | A6 — Address input |
| Broche 5 | A5 — Address input |
| Broche 6 | A4 — Address input |
| Broche 7 | A3 — Address input |
| Broche 8 | A2 — Address input |
| Broche 9 | A1 — Address input |
| Broche 10 | A0 — Address input |
| Broche 11 | O0 — Data output 0 |
| 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 |
| Broche 20 | CE — Chip enable |
| Broche 21 | A10 — Address input |
| Broche 22 | OE — Output enable |
| Broche 23 | A11 — Address input |
| Broche 24 | A9 — Address input |
| Broche 25 | A8 — Address input |
| Broche 26 | A13 — Address input |
| Broche 27 | A14 — Address input |
| Broche 28 | VCC — Power supply (5 V) |
Applications typiques
27C256A-12 convient pour 6 applications: Embedded Firmware Storage, Retro Arcade and Console Repair, Industrial Control Equipment, Legacy BIOS and Boot Code Storage, Telecommunications Equipment, Test and Measurement Instruments.
Embedded Firmware Storage
The 27C256A-12 stores boot and application firmware for 8-bit microcontrollers and microprocessors such as the Z80, 8051, and 6809 families. Its 32K x 8 organization maps directly to a single 32 KB code space, and the 120 ns access time supports zero-wait-state fetches with most classic CPU clock speeds up to roughly 8 MHz. As a CMOS device it draws minimal standby current, an advantage in battery-backed or always-on industrial controllers. Code is burned once with a programmer and remains fixed for the product life, which suits certified or safety-adjacent equipment where field firmware changes are undesirable.
Recommandé
Retro Arcade and Console Repair
Original arcade boards, home consoles, and pinball machines from the 1980s and 1990s commonly used 27C256-family EPROMs for program and graphics ROMs. The 27C256A-12, with its 120 ns access and standard DIP-28 footprint, is a preferred authentic replacement when restoring these boards. Technicians dump the original ROM, verify the CRC against known-good dumps, and program a new 27C256A-12. Because failing EPROMs exhibit bit rot after decades, replacing them with freshly programmed CMOS parts restores reliability while preserving original board aesthetics and socket compatibility.
Recommandé
Industrial Control Equipment
Programmable logic controllers, motor drive controllers, and instrumentation from legacy industrial lines store their operating code in 27C256 EPROMs. The 27C256A-12 tolerates the electrically noisy industrial environment because its read-only storage is immune to corruption from power glitches, unlike RAM-based code storage. Its 5 V supply integrates directly into legacy 5 V logic rails, and the 120 ns access time meets the timing of typical 68000-family and Z180 control processors. When a controller EPROM fails, a replacement 27C256A-12 programmed from archived firmware images restores the unit to factory configuration.
Recommandé
Legacy BIOS and Boot Code Storage
PC motherboards, expansion cards such as SCSI and network adapters, and single-board computers of the 286/386 era used 27C256 EPROMs to hold BIOS and option ROM code. The 27C256A-12 provides the exact 32 KB capacity of many option ROM images. Engineers maintaining or replicating vintage computing hardware use this device to reproduce authentic BIOS chips; the 120 ns access time matches ISA-bus era timing requirements. UV-erasability allows iteration during BIOS reverse-engineering or localization projects, though flash-based pin-compatible substitutes are often chosen for repeated reprogramming.
Recommandé
Telecommunications Equipment
Channel banks, PBX line cards, modems, and test sets from the pre-flash era stored firmware and country-configuration tables in 27C256 EPROMs. The 27C256A-12s CMOS technology reduces power consumption across cards with dozens of memory devices, and its non-volatile read-only nature guarantees configuration integrity through power cycles. Its standard parallel interface requires no controller overhead, and the -12 speed grade accommodates the 8-16 MHz processor clocks common in telecom hardware. Service organizations keep programmed 27C256A-12 stock to field-replace firmware chips without returning cards to depots.
Recommandé
Test and Measurement Instruments
Oscilloscopes, logic analyzers, and calibration fixtures from the 1990s embed 27C256 EPROMs holding self-test routines, calibration tables, and instrument firmware. The 27C256A-12 provides stable, corruption-immune storage for calibration constants that must survive decades; unlike EEPROM, its contents cannot drift under read stress. Its 120 ns access time supports the fast diagnostic sequencers used at instrument power-up. Calibration laboratories reproducing legacy instrument firmware program 27C256A-12 devices from archived images to keep discontinued test equipment serviceable, avoiding costly hardware replacement of still-accurate measurement front ends.
Recommandé
Récapitulatif des produits recommandés
Données de référence d'ingénierie pour 27C256A-12 — comparaison, recommandations de conception et informations de conformité.
Guide de sélection
Comparaison avec les alternatives
| Paramètre | Ce produit | 27C256L-20R | 27C256T-15/SO | 27C256A12A | 27C512-10 |
|---|---|---|---|---|---|
| Package | 28-pin DIP | 28-pin DIP - same | 28-pin SOIC | 28-pin DIP - same | 28-pin DIP - same |
| Brand | NEC | Microchip Technology | Microchip Technology | NXP Semiconductors | Microchip Technology |
| Memory Size | 256 Kbit (32K x 8) | 256 Kbit (32K x 8) | 256 Kbit (32K x 8) | 256 Kbit (32K x 8) | 512 Kbit (64K x 8) |
| Access Time | 120 ns | 200 ns | 150 ns | 120 ns | 100 ns |
| Technology | CMOS | CMOS | CMOS | CMOS | CMOS |
| Supply Voltage | 5 V | 5 V | 5 V | 5 V | 5 V |
| Mounting Type | Through Hole | Through Hole | Surface Mount | Through Hole | Through Hole |
| Lifecycle Status | Obsolete | Obsolete / aftermarket | Obsolete / aftermarket | Obsolete / aftermarket | Obsolete / aftermarket |
Principaux différenciateurs
- Fastest common speed grade in 27C256 family (vs 27C256L-20R)
- True same-speed cross-brand equivalent available (vs 27C256A12A)
- Native 32K x 8 density without address strapping (vs 27C512-10)
Notes de conception
Do not assume all 27C256 devices share a programming algorithm. NEC, Philips/NXP, Microchip, and Fujitsu variants differ in VPP level (commonly 12.5 V or 21 V), program pulse width, and verify procedures. Programming a 27C256A-12 with the wrong VPP or algorithm can permanently damage the part or produce unreliable data retention. Always read the datasheet of the actual manufacturer of the specific chip in hand before programming, and verify the programmed image with a checksum or CRC read-back.
At 120 ns access time, trace delay and output loading matter in larger systems. Keep address and data traces under roughly 20 cm between the EPROM and processor, and limit each output line to a few CMOS loads to preserve the access-time budget. Decouple VCC with a 0.1 uF ceramic capacitor directly at pins 28/14. If the bus is lightly buffered, the CE-to-output access (tCE) often dominates over tAA, so check both figures against your CPU wait-state generation.
When retrofitting a 27C512 into a 27C256 socket to gain capacity or availability, strap the extra address line A15 (pin 1 on the 27C512 JEDEC pinout) appropriately: high for the upper 32K block or low for the lower block. On the 27C256 the same pin is VPP, so confirm the socket signal at pin 1 is within safe levels for the substituted device. For UV windowed parts in exposed environments, cover the window with an opaque label to prevent slow UV-induced data erasure from sunlight and fluorescent lighting.
Informations de conformité
Part predates RoHS/REACH regulation and is discontinued; no compliance data is published by distributors. Repair-of-legacy-equipment exemptions may apply.
