27C256-120N - 32Kx8 120ns CMOS EPROM | ASI | Legacy Memory
MPN: 27C256-120N β End of Life| Qty | Unit Price | Extended |
|---|---|---|
| 1 | $2.95 | $2.95 |
| 10 | $2.6 | $26.00 |
| 100 | $2.25 | $225.00 |
| 500 | $1.95 | $975.00 |
| 1,000 | $1.75 | $1,750.00 |
Drop-in alternatives for 27C256-120N β same package, pin-to-pin compatible. Different-package parts requiring PCB rework are excluded.
Quick Comparison Tool β Select alternative parts for side-by-side comparison:
27C256-12/L
β Drop-Inβ In Stock
$3.9 / Unit
View Datasheet β27C256A-12
β Drop-Inβ In Stock
$2.52 / Unit
View Datasheet β27C256T-15/SO
β Drop-Inβ In Stock
$1.9 / Unit
View Datasheet βM27C256B-12F1
β Drop-Inπ Reference alternative (not in catalog)
NM27C256N120
β Drop-Inπ Reference alternative (not in catalog)
MX27C256
β Drop-Inπ Reference alternative (not in catalog)
CY27C256
β Drop-Inπ Reference alternative (not in catalog)
AT29C256
β Drop-Inπ Reference alternative (not in catalog)
27C256-120N Maximum Ratings & Electrical Characteristics
| Memory Organization | 32K x 8 bit (256 Kbit) |
| Access Time | 120 ns |
| Technology | CMOS EPROM (UV erasable) |
| Supply Voltage (Read) | 5 V +/-10% |
| Standby Current | 20 uA typical (CMOS standby) |
| Programming Method | 100% Flashrite programming |
| Pinout | JEDEC-approved 27C256 pinout |
| Package | 28-pin plastic DIP (DIP-28) |
| Erase Method | Ultraviolet light (quartz window / windowed variant) |
| Mounting Type | Through Hole |
| Output Type | Parallel, 3-state outputs |
| Control Signals | CE, OE, PGM |
| Lifecycle Status | End of Life (per Futurlec) |
27C256-120N Pin Configuration
| Pin 1 | VPP β Programming supply voltage |
| Pin 2 | A12 β Address input bit 12 |
| Pin 3 | A7 β Address input bit 7 |
| Pin 4 | A6 β Address input bit 6 |
| Pin 5 | A5 β Address input bit 5 |
| Pin 6 | A4 β Address input bit 4 |
| Pin 7 | A3 β Address input bit 3 |
| Pin 8 | A2 β Address input bit 2 |
| Pin 9 | A1 β Address input bit 1 |
| Pin 10 | A0 β Address input bit 0 |
| Pin 11 | O0 β Data output bit 0 (3-state) |
| Pin 12 | O1 β Data output bit 1 (3-state) |
| Pin 13 | O2 β Data output bit 2 (3-state) |
| Pin 14 | GND β Ground reference |
| Pin 15 | O3 β Data output bit 3 (3-state) |
| Pin 16 | O4 β Data output bit 4 (3-state) |
| Pin 17 | O5 β Data output bit 5 (3-state) |
| Pin 18 | O6 β Data output bit 6 (3-state) |
| Pin 19 | O7 β Data output bit 7 (3-state) |
| Pin 20 | CE β Chip enable (device select) |
| Pin 21 | A10 β Address input bit 10 |
| Pin 22 | OE β Output enable |
| Pin 23 | A11 β Address input bit 11 |
| Pin 24 | A9 β Address input bit 9 |
| Pin 25 | A8 β Address input bit 8 |
| Pin 26 | A13 β Address input bit 13 |
| Pin 27 | PGM β Program enable pulse |
| Pin 28 | VCC β +5 V power supply |
Safe Operating Area (SOA) & Thermal Characteristics
No official SOA curve available for this digital IC. Always operate within absolute maximum ratings specified in the datasheet. Ensure adequate cooling and derate as needed.
Typical Applications
27C256-120N is suitable for 6 applications: Legacy Embedded Firmware Storage, Retro Computing and Arcade Repair, Industrial Control and PLC Legacy Boards, Automotive ECU and Module Firmware, Telecommunications Line Cards, Test and Measurement Instrument Firmware.
Legacy Embedded Firmware Storage
The 27C256-120N stores boot code and application firmware in 8-bit and 16-bit microcontroller systems designed in the 1980s-1990s. Its 120 ns access time meets the zero-wait-state bus timing of classic MC68000, Z80, and 8051-family designs, while the JEDEC 27C256 pinout matches the sockets already on those boards. Non-volatile UV EPROM storage guarantees code integrity across power cycles with no wear-out mechanism, unlike Flash. With 20 uA typical CMOS standby current, the memory adds negligible load to battery-backed equipment. For field-updatable products, pair with a socketed, windowed device so firmware revisions can be erased and reprogrammed at the bench.
Recommended
Retro Computing and Arcade Repair
Retro computer motherboards, arcade game PCBs, and pinball controllers rely on 27C256 sockets for ROM code. The 27C256-120N drops directly into these sockets because the JEDEC DIP-28 pinout (VPP, CE, OE, PGM) is identical across all 27C256 manufacturers. Its 120 ns speed satisfies the bus timing of period hardware that assumed 150-250 ns NMOS parts, so it is always timing-safe. Community resources such as minuszerodegrees.net document exact socket caveats when using Flash substitutes, reinforcing why true EPROMs remain preferred for authentic repairs. Burned-from-image devices restore machines to factory behavior without counterfeit ROM risk.
Recommended
Industrial Control and PLC Legacy Boards
Long-lifecycle industrial equipment - PLCs, motor drives, process controllers - was designed around UV EPROM firmware and remains in service for decades. The 27C256-120N sustains these fleets: a single +5 V supply with +/-10% tolerance tolerates noisy factory power rails, and the 20 uA standby current suits battery-backed memory-retention schemes. Replacement of failed EPROMs with the same JEDEC-pinout family (ST M27C256B, Microchip 27C256) requires no board modification. Because the device is electrically read-only, its contents cannot be corrupted by transients, an inherent reliability advantage over electrically writable alternatives in high-EMI environments.
Recommended
Automotive ECU and Module Firmware
Classic automotive ECUs, engine management boards, and instrument clusters used 27C256 devices for calibration maps and code. The 27C256-120N in plastic DIP is electrically read-only, so its calibration data survives under-hood transients and cannot be overwritten by faults - one reason OEMs chose EPROMs. Chipsport-style tuning communities re-burn these devices with revised maps; windowed variants allow iterative erase/program cycles on the bench. The 120 ns access time meets 8-bit MCU bus timing in these modules. For identical sockets, all JEDEC-pinout 27C256 manufacturers' parts are interchangeable, simplifying repair sourcing for discontinued vehicles.
Recommended
Telecommunications Line Cards
Vintage telecom line cards, modems, and PBX control boards stored firmware and lookup tables in 27C256 EPROMs. The device's single +5 V read supply and JEDEC pinout integrate into these card designs directly, and its CMOS split-gate cell keeps board-level power low across densely populated cards - 20 uA standby per device scales well versus NMOS predecessors. The 120 ns access time supports the processor cycles of T1/E1 and modem-era control logic. Spares stocked now extend the life of installed telecom base for carriers maintaining legacy central-office equipment whose replacement cost far exceeds the memory component cost.
Recommended
Test and Measurement Instrument Firmware
Oscilloscopes, logic analyzers, and signal generators of the EPROM era stored system firmware in 27C256-class devices. The 27C256-120N's deterministic read timing (120 ns access, 3-state outputs under CE/OE control) suits the disciplined bus designs of instrumentation, and its non-volatile read-only nature guarantees the instrument boots with its calibrated code every time. Repair shops restoring such instruments burn verified firmware images into windowed 27C256 devices, erase with UV, and re-cycle as needed during bring-up. Cross-manufacturer JEDEC compatibility means an ST or Microchip part replaces the original ASI device without rework.
Recommended
Recommended Products Summary
Engineering reference data for 27C256-120N β comparison, design guidance, and compliance information.
Selection Guide
Comparison with Alternatives
| Parameter | This Product | 27C256-12/L | M27C256B-12F1 | NM27C256N120 | AT29C256 |
|---|---|---|---|---|---|
| Package | DIP-28 | DIP-28 - same | DIP-28 - same | DIP-28 - same | DIP-28 - same |
| Brand | ASI | Microchip Technology | STMicroelectronics | Fairchild | Microchip Technology (Atmel) |
| Access Time | 120 ns | 120 ns | 120 ns | 120 ns | 70 ns |
| Organization | 32K x 8 | 32K x 8 | 32K x 8 | 32K x 8 | 32K x 8 |
| Technology | CMOS UV EPROM | CMOS UV EPROM | CMOS UV EPROM | CMOS split-gate UV EPROM | CMOS Flash |
| Erase Method | UV light | UV light | UV light | UV light | Electrical (in-system) |
| Standby Current | 20 uA typical | [DATA_NEEDED] | [DATA_NEEDED] | [DATA_NEEDED] | [DATA_NEEDED] |
| Pin 1 Function | VPP | VPP - same | VPP - same | VPP - same | A14 (or WE) - differs |
| Supply Voltage | 5 V +/-10% | 5 V +/-10% | 5 V +/-10% | 5 V +/-10% | 5 V +/-10% |
| Lifecycle | EOL | EOL / residual stock | EOL / residual stock | Obsolete | EOL / residual stock |
Key Differentiators
- Guaranteed JEDEC 27C256 pinout compatibility (vs AT29C256)
- Lower standby power than NMOS predecessors (vs NM27C256N120)
- Electrically read-only robustness (vs AT29C256)
Design Notes
Do not substitute an AT28C256/AT29C256 Flash into a 27C256 socket without checking pin 1: in most 27C256 sockets pin 1 is tied to +5V (VPP), but on the AT28C256 pin 1 is A14, so the first half of the device mirrors the second half from the host's perspective (per minuszerodegrees.net). Either rework the socket so pin 1 is switchable to A14, or burn an image whose first and second halves are duplicated.
The 120 ns access time is measured from valid address to valid output with CE/OE asserted. In long bus or backplane designs, subtract trace propagation and output-loading delays: if address setup plus propagation approaches 120 ns, move to a faster grade (90 ns NM27C256 or 70 ns AT29C256) rather than risking marginal reads. Add 0.1 uF decoupling at the VCC pin (pin 28) to suppress bus switching noise on the 3-state outputs.
For new boards accepting either EPROM or Flash, route pin 1 (VPP) through a jumper or pull-up to VCC with the option to connect to a socket at A14 instead. This makes the same footprint compatible with 27C256 EPROMs and AT29C256-class Flash, future-proofing against end-of-life - particularly important since the entire 27C256 family is EOL per Futurlec and all UV EPROM manufacturing has ceased industry-wide.
Compliance Information
Part is discontinued and pre-dates RoHS enforcement; legacy stock may be leaded construction. Request certificate of conformity from the specific seller.
