27C256L-20R - 256Kbit 32Kx8 CMOS EPROM 200ns | WSI
MPN: 27C256L-20R β End of Life| Qty | Unit Price | Extended |
|---|---|---|
| 1 | $3.2 | $3.20 |
| 10 | $2.88 | $28.80 |
| 100 | $2.45 | $245.00 |
| 500 | $2.1 | $1,050.00 |
| 1,000 | $1.85 | $1,850.00 |
Drop-in alternatives for 27C256L-20R 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:
27C256L-20
β Drop-In β οΈ εζ°εΎ ιͺθ―π Reference alternative (not in catalog)
27C256L-15
β Drop-In β οΈ εζ°εΎ ιͺθ―π Reference alternative (not in catalog)
27C256T-20
β Drop-In β οΈ εζ°εΎ ιͺθ―π Reference alternative (not in catalog)
27C256-20
β Drop-In β οΈ εζ°εΎ ιͺθ―π Reference alternative (not in catalog)
27C256T-15/SO
β Drop-Inβ In Stock
$1.9 / Unit
View Datasheet β27C256L-20R Maximum Ratings & Electrical Characteristics
| Memory Size | 256 Kilobit |
| Organization | 32K x 8-bit |
| Memory Type | CMOS EPROM (UV erasable) |
| Access Time | 200 ns (-20 speed grade) |
| Supply Voltage | Single +5 V with +/-10% tolerance |
| Standby Current | 20 uA typical (CMOS standby) |
| Programming Scheme | 100% Flashrite programming |
| Pinout | JEDEC-approved 28-pin pinout |
| Address Lines | A0 to A14 (15 lines) |
| Data Lines | O0 to O7 (8 lines) |
| Control Signals | CE, OE, PGM/VPP |
| Package | 28-pin package (per JEDEC EPROM pinout) |
| Mounting Type | Through-Hole |
| Erase Method | Ultraviolet light (UV EPROM) |
27C256L-20R Pin Configuration
| Pin 1 | VPP β Program supply voltage |
| Pin 2 | A12 β Address input |
| Pin 3 | A7 β Address input |
| Pin 4 | A6 β Address input |
| Pin 5 | A5 β Address input |
| Pin 6 | A4 β Address input |
| Pin 7 | A3 β Address input |
| Pin 8 | A2 β Address input |
| Pin 9 | A1 β Address input |
| Pin 10 | A0 β Address input |
| Pin 11 | O0 β Data output 0 |
| Pin 12 | O1 β Data output 1 |
| Pin 13 | O2 β Data output 2 |
| Pin 14 | GND β Ground |
| Pin 15 | O3 β Data output 3 |
| Pin 16 | O4 β Data output 4 |
| Pin 17 | O5 β Data output 5 |
| Pin 18 | O6 β Data output 6 |
| Pin 19 | O7 β Data output 7 |
| Pin 20 | CE β Chip enable |
| Pin 21 | A10 β Address input |
| Pin 22 | OE β Output enable |
| Pin 23 | A11 β Address input |
| Pin 24 | A9 β Address input |
| Pin 25 | A8 β Address input |
| Pin 26 | A13 β Address input |
| Pin 27 | PGM β Program enable |
| Pin 28 | VCC β Power supply (+5 V) |
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
27C256L-20R is suitable for 6 applications: Legacy Firmware / BIOS Storage, Industrial Control Boards, Automotive ECU Repair (Legacy), Telecom Equipment, Obsolete Component Replacement / Repair, Embedded Systems Education and Prototyping.
Legacy Firmware / BIOS Storage
The 27C256L-20R stores boot firmware and BIOS code in legacy computer and embedded controller boards that use 28-pin EPROM sockets. Its 32K x 8 organization holds a full 32 KB BIOS image, and the 200 ns access time meets the timing of mid-1980s to 1990s microprocessors without wait states. Because the device is UV-erasable, service technicians can re-program firmware revisions on the same socket using the Flashrite programming scheme. For retrofit work, any 27C256-family part with -20 or faster speed grade is a pin-compatible substitute, preserving board-level layout and socket compatibility.
Recommended
Industrial Control Boards
Industrial PLCs, motor controllers, and process-control boards of the pre-Flash era commonly used 27C256 EPROMs to hold ladder-logic interpreters and control firmware. The 27C256L-20R fits this role with its single +5 V supply and +/-10% tolerance, which tolerates industrial power rails without a regulator change, and its 20 uA typical CMOS standby current reduces draw in battery-backed or low-duty-cycle controllers. Maintenance teams benefit from UV reprogrammability when control logic must be revised without redesigning the PCB, making the part a standard spares item for aging factory equipment.
Recommended
Automotive ECU Repair (Legacy)
Engine control units from the 1980s and early 1990s frequently carried a 28-pin EPROM holding fuel and ignition maps. The 27C256L-20R serves as a repair and re-mapping device: technicians erase the original calibration under UV light and program updated lookup tables with an EPROM programmer using the Flashrite algorithm. The 200 ns access time satisfies typical ECU processor bus timing, and the JEDEC pinout guarantees socket compatibility. Because the L variant draws only 20 uA typical standby, it is also appropriate for keep-alive memory roles where modest battery-backed retention matters.
Recommended
Telecom Equipment
Line cards, PBX controllers, and modems of the EPROM era used 27C256 devices for protocol and configuration code. The 27C256L-20R provides byte-wide non-volatile storage with deterministic 200 ns read timing, important for processors without cache that fetch code directly from ROM. The +/-10% supply tolerance suits telecom -48 V-derived 5 V rails with switching ripple, and CMOS standby keeps board-level power within budget when the device is deselected. Its JEDEC pinout means a failed device can be replaced or re-programmed in the field without PCB modification.
Recommended
Obsolete Component Replacement / Repair
Repair shops maintaining aging test instruments, arcade boards, medical devices, and avionics trainers routinely need a 32K x 8 EPROM to replace a failed or lost-program device. The 27C256L-20R is the canonical choice: its JEDEC-approved 28-pin pinout is shared across every 27C256 manufacturer variant, so a replacement programs and reads identically regardless of the original brand. The 100% Flashrite programming scheme minimizes bench programming time when building small batches of replacement ROMs. Keeping a stock of -20 or faster grades covers virtually every 32 KB socket encountered in service work.
Recommended
Embedded Systems Education and Prototyping
The 27C256L-20R remains popular in university microprocessor labs and hobbyist retro-computing projects because it demonstrates fixed-memory fundamentals: address decoding across 15 address lines, CE/OE control timing, and UV erasure as a tangible view of non-volatile storage. With 200 ns access time and a single +5 V supply, it interfaces directly to classic 8-bit CPUs such as the Z80 and 6502 without glue-logic speed concerns. Students can erase, program, and re-run firmware cycles, building an intuitive understanding of memory-mapped code storage that Flash-based designs obscure.
Recommended
Recommended Products Summary
Engineering reference data for 27C256L-20R β comparison, design guidance, and compliance information.
Selection Guide
Comparison with Alternatives
| Parameter | This Product | 27C256L-20 | 27C256L-15 | 27C256T-20 | 27C256 |
|---|---|---|---|---|---|
| Package | 28-pin DIP (JEDEC EPROM) | 28-pin DIP (JEDEC EPROM) - same | 28-pin DIP (JEDEC EPROM) - same | 28-pin DIP (JEDEC EPROM) - same | 28-pin DIP (JEDEC EPROM) - same |
| Brand | WSI (WaferScale Integration) | WSI (WaferScale Integration) | WSI (WaferScale Integration) | WSI (WaferScale Integration) | Microchip Technology |
| Organization | 32K x 8-bit | 32K x 8-bit | 32K x 8-bit | 32K x 8-bit | 32K x 8-bit |
| Access Time | 200 ns | 200 ns | 150 ns | 200 ns | [DATA_NEEDED] |
| Supply Voltage | Single +5 V +/-10% | Single +5 V +/-10% | Single +5 V +/-10% | Single +5 V +/-10% | Single +5 V +/-10% |
| Standby Current | 20 uA typical (CMOS) | 20 uA typical (CMOS) | 20 uA typical (CMOS) | [DATA_NEEDED] | [DATA_NEEDED] |
| Programming Scheme | 100% Flashrite | 100% Flashrite | 100% Flashrite | 100% Flashrite | [DATA_NEEDED] |
| Memory Size | 256 Kilobit | 256 Kilobit | 256 Kilobit | 256 Kilobit | 256 Kilobit |
Key Differentiators
- Low-power CMOS standby core (vs 27C256-20)
- Cost-effective 200 ns speed grade (vs 27C256L-15)
- Reel packaging for production runs (vs 27C256L-20)
Design Notes
The 27C256L-20R operates from a single +5 V supply with a standard +/-10% tolerance (4.5 V to 5.5 V). Decouple VCC with a 0.1 uF ceramic capacitor close to pin 28 and pin 14 ground return. During programming, VPP (pin 1) must be raised to the programming voltage specified in the manufacturer datasheet - never leave VPP tied to a high voltage in read mode, as this can damage the device or corrupt contents. Estimated: with 20 uA typical CMOS standby current, battery-backed standby power is only about 0.1 mW at 5 V.
Verify the host processor bus timing against the 200 ns access time of the -20 grade. Access time is measured from address valid or from CE/OE falling edge - whichever constraint applies. If the processor cycle time minus address setup leaves less than 200 ns, insert a wait state or select a faster grade (27C256L-15 at 150 ns is pin-compatible). Unused address/data lines should follow standard CMOS practice; the eight outputs drive standard TTL/CMOS loads directly.
UV EPROMs are frequently damaged by programming with incorrect VPP levels or by erasing with an underpowered UV lamp. Use a calibrated programmer implementing the 100% Flashrite algorithm and confirm the quartz window is fully exposed during erasure - a partially covered window yields incomplete erase and intermittent bit errors that mimic device failure. Because WSI is defunct, authenticate broker-supplied parts: remarked or counterfeit 27C256 devices are common in the obsolete market. Mark programmed devices with an opaque label over the window to prevent sunlight-induced gradual data loss.
Compliance Information
Compliance data not available in verified sources; WSI is defunct and this part is obsolete, so formal compliance documentation is generally unobtainable.
