27C256A-12 - 256Kbit CMOS EPROM 32Kx8 120ns | NEC
料号： 27C256A-12 ✗ 停产| 数量 | 单价 | 小计 |
|---|---|---|
| 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 概述
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.
直接替换替代料： 27C256A-12 ——相同封装，引脚兼容。需要 PCB 改动的不同封装料号已排除。
本系列中的变体
可与以下型号直接替换的同系列型号： 27C256A-12 （相同外形与封装尺寸） ——差异在于 Package, Memory Type, Organization, Erase Method, Mounting Type.
快速对比工具——选择替代料号进行并排对比：
27C256L-20R
✅ 直接替换✓ 有现货
$1.85 / 个
查看数据手册 →27C256T-15/SO
✅ 直接替换✓ 有现货
$1.9 / 个
查看数据手册 →27C256A12A
✅ 直接替换📋 参考替代料（不在目录中）
27C256A-12 最大额定值与电气特性
| 存储器类型 | UV EPROM |
| Technology | CMOS |
| 存储容量 | 256 Kbit (32K x 8) |
| 存储组织 | 32K x 8 |
| Access Time | 120 ns |
| Supply Voltage (VCC) | 5 V |
| 接口 | Parallel |
| 工作温度 | 0C to +70C (commercial) |
| 封装 | 28-pin DIP |
| 安装类型 | Through Hole |
| Erase Method | Ultraviolet light |
| RoHS 状态 | unknown |
| 生命周期状态 | Obsolete (legacy product) |
27C256A-12 引脚配置
| 引脚 1 | VPP — Programming supply voltage / program enable |
| 引脚 2 | A12 — Address input |
| 引脚 3 | A7 — Address input |
| 引脚 4 | A6 — Address input |
| 引脚 5 | A5 — Address input |
| 引脚 6 | A4 — Address input |
| 引脚 7 | A3 — Address input |
| 引脚 8 | A2 — Address input |
| 引脚 9 | A1 — Address input |
| 引脚 10 | A0 — Address input |
| 引脚 11 | O0 — Data output 0 |
| 引脚 12 | O1 — Data output 1 |
| 引脚 13 | O2 — Data output 2 |
| 引脚 14 | GND — Ground |
| 引脚 15 | O3 — Data output 3 |
| 引脚 16 | O4 — Data output 4 |
| 引脚 17 | O5 — Data output 5 |
| 引脚 18 | O6 — Data output 6 |
| 引脚 19 | O7 — Data output 7 |
| 引脚 20 | CE — Chip enable |
| 引脚 21 | A10 — Address input |
| 引脚 22 | OE — Output enable |
| 引脚 23 | A11 — Address input |
| 引脚 24 | A9 — Address input |
| 引脚 25 | A8 — Address input |
| 引脚 26 | A13 — Address input |
| 引脚 27 | A14 — Address input |
| 引脚 28 | VCC — Power supply (5 V) |
典型应用
27C256A-12 适用于 6 应用s: 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.
推荐
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.
推荐
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.
推荐
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.
推荐
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.
推荐
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.
推荐
推荐产品汇总
工程参考数据： 27C256A-12 ——对比、设计指导和合规信息。
选型指南
与替代料对比
| 参数 | 本产品 | 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 |
关键差异点
- Fastest common speed grade in 27C256 family （对比 27C256L-20R)
- True same-speed cross-brand equivalent available （对比 27C256A12A)
- Native 32K x 8 density without address strapping （对比 27C512-10)
设计说明
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.
合规信息
Part predates RoHS/REACH regulation and is discontinued; no compliance data is published by distributors. Repair-of-legacy-equipment exemptions may apply.
