27C256L-12TMB - 32Kx8 Military CMOS EPROM 120ns | WSI/ST
N.º de pieza: 27C256L-12TMB ✗ Fin de vida| Cant. | Precio unitario | Total |
|---|---|---|
| 1 | $12.5 | $12,50 |
| 10 | $11.2 | $112,00 |
| 100 | $9.8 | $980,00 |
| 500 | $8.9 | $4.450,00 |
| 1.000 | $8.25 | $8.250,00 |
27C256L-12TMB Descripción general
An EPROM is a non-volatile memory device programmed electrically and erased only by exposure to ultraviolet light through a quartz window. Within the memory hierarchy, the EPROM belongs to the UV PROM family, predating EEPROM and Flash memory, and remains relevant in legacy military, aerospace, and avionics systems where long-term availability and radiation-tolerant ceramic packaging are required.
Key features of this device include the 256K-bit organization (32,768 words by 8 bits), a fast 120 ns maximum access time, advanced CMOS technology for low static power consumption, TTL-compatible I/O levels, and tri-state output buffers controlled by dual-output-enable logic. The ceramic CLLCC construction supports military screening levels and wide temperature operation beyond commercial plastic-packaged equivalents.
Technically, the device uses a CMOS cell array with address decoders for 15 address lines (A0 through A14), eight data outputs, a chip-enable input, and output-enable controls. When CE or OE is deasserted high, the I/O pins enter a high-impedance state, simplifying bus sharing in microprocessor systems.
Typical applications include legacy military equipment, avionics program storage, embedded 8-bit and 16-bit microprocessor boot code, industrial control retrofits, and obsolescence-driven replacement purchases for fielded hardware.
Design consideration: because EPROM programming requires a separate VPP supply and erasure is via UV light, designers maintaining legacy systems should verify programmer compatibility and keep programmed spares, as re-programming in the field is impractical.
This page synthesizes distributor availability, drop-in alternative MPNs, and practical design guidance not consolidated in the manufacturer datasheet, adding sourcing value for buyers maintaining military legacy programs.
Alternativas directas para 27C256L-12TMB — mismo encapsulado, compatible pin a pin. Se excluyen las piezas de otro encapsulado que requieren retrabajo de la PCB.
Variantes de esta serie
Modelos de la misma serie compatibles directamente con 27C256L-12TMB (mismo factor de forma y huella) — difiere en Package, Memory Type, Mounting Type, Memory Size, Organization.
Herramienta de comparación rápida — seleccione piezas alternativas para compararlas lado a lado:
WS27C256L-12TMB
✅ Sustitución directa📋 Alternativa de referencia (no en el catálogo)
27C256L-12TMB
✅ Sustitución directa✓ En stock
$8.25 / unidad
Ver hoja de datos →WS27C256L-15TMB
✅ Sustitución directa ⚠️ Especificaciones sin verificar📋 Alternativa de referencia (no en el catálogo)
WS27C256L-12JI
✅ Sustitución directa ⚠️ Especificaciones sin verificar📋 Alternativa de referencia (no en el catálogo)
27C256A-12
✅ Sustitución directa ⚠️ Especificaciones sin verificar✓ En stock
$2.52 / unidad
Ver hoja de datos →27C256T-15/SO
✅ Sustitución directa ⚠️ Especificaciones sin verificar✓ En stock
$1.9 / unidad
Ver hoja de datos →27C256L-12TMB Valores máximos y características eléctricas
| Tamaño de memoria | 256 Kbit |
| Organización de memoria | 32K x 8 |
| Access Time | 120 ns |
| Supply Voltage (VCC) | 4.5 V to 5.5 V |
| Minimum Supply Voltage | 4.5 V |
| Technology | CMOS |
| Tipo de memoria | UV EPROM |
| Temperature Grade | Military |
| Encapsulado | 28-pin Ceramic Leadless Chip Carrier (CLLCC) |
| Number of Terminals | 28 |
| Package Shape | Rectangular |
| Address Lines | 15 (A0 to A14) |
| Data Outputs | 8, tri-state |
| Tipo de montaje | Surface Mount |
| I/O Level | TTL compatible |
| Estado RoHS | unknown |
Configuración de pines de 27C256L-12TMB
| Pin 1 | A7 — Address input bit 7 |
| Pin 2 | A6 — Address input bit 6 |
| Pin 3 | A5 — Address input bit 5 |
| Pin 4 | A4 — Address input bit 4 |
| Pin 5 | A3 — Address input bit 3 |
| Pin 6 | A2 — Address input bit 2 |
| Pin 7 | A1 — Address input bit 1 |
| Pin 8 | A0 — Address input bit 0 |
| Pin 9 | Q0 — Data output bit 0 (tri-state) |
| Pin 10 | Q1 — Data output bit 1 (tri-state) |
| Pin 11 | Q2 — Data output bit 2 (tri-state) |
| Pin 12 | GND — Ground |
| Pin 13 | Q3 — Data output bit 3 (tri-state) |
| Pin 14 | Q4 — Data output bit 4 (tri-state) |
| Pin 15 | Q5 — Data output bit 5 (tri-state) |
| Pin 16 | Q6 — Data output bit 6 (tri-state) |
| Pin 17 | Q7 — Data output bit 7 (tri-state) |
| Pin 18 | CE — Chip enable |
| Pin 19 | A10 — Address input bit 10 |
| Pin 20 | OE — Output enable |
| Pin 21 | VPP — Programming voltage supply |
| Pin 22 | A8 — Address input bit 8 |
| Pin 23 | A9 — Address input bit 9 |
| Pin 24 | A11 — Address input bit 11 |
| Pin 25 | A12 — Address input bit 12 |
| Pin 26 | A13 — Address input bit 13 |
| Pin 27 | A14 — Address input bit 14 |
| Pin 28 | VCC — Power supply, 4.5 V to 5.5 V |
Aplicaciones típicas
27C256L-12TMB es adecuado para 6 aplicacións: Military Avionics Program Storage, Legacy Embedded Boot ROM, Industrial Control Retrofit, Defense Obsolescence Replacement, Test Equipment Firmware Modules, Character Generator and Lookup Tables.
Military Avionics Program Storage
The 27C256L-12TMB was designed specifically for military avionics program storage, where its ceramic leadless chip carrier (CLLCC) package, military temperature grade, and 120 ns access time align with the reliability and timing requirements of flight-control processors and mission computers. In this role, the 32K x 8 organization stores boot code or application firmware for 8-bit and 16-bit processors, with the tri-state outputs sharing the processor bus under CE/OE control. Because the part is EOL, sustainment programs typically buy and program a pool of spares; the UV window allows verified reprogramming of returned units, and the ceramic construction withstands the thermal cycling profiles typical of avionics enclosures better than plastic packages.
Recomendado
Legacy Embedded Boot ROM
In legacy embedded systems, the 27C256L-12TMB serves as boot ROM: its 120 ns access time permits zero-wait-state fetch from reset for processors such as the 80C31, 68HC11, and early 68000 derivatives. The 15 address lines (A0-A14) map directly to the processor address bus, and TTL-compatible outputs drive the data bus without level shifters at 5 V. The CMOS process keeps static power low, important in conduction-cooled military enclosures. Designers maintaining these boards should confirm the programmer supports the 27C256 family algorithm and VPP requirement, and should store programmed spares with UV-opaque labels to prevent accidental bit corruption from fluorescent lighting or sunlight exposure.
Recomendado
Industrial Control Retrofit
Factory automation and process-control equipment built in the 1980s and 1990s used 27C256-family EPROMs for firmware storage, and fielded controllers still require form-fit-function replacements during overhaul. The 27C256L-12TMB fits the original 28-pin CLCC socket without board modification, restoring the 120 ns access time that older CPU boards expect. Because the device is erased by UV and programmed once in-house, maintenance shops can keep a small inventory of blank parts plus a legacy programmer, updating firmware revisions by reprogramming erasable parts instead of scrapping boards. Its military screening also suits industrial environments with wide ambient temperature swings near furnaces or outdoor installations.
Recomendado
Defense Obsolescence Replacement
Defense logistics organizations use the 27C256L-12TMB as an authorized obsolescence replacement when the original WSI, STMicroelectronics, or e2v date-code stock is exhausted. Distributor cross-reference data confirms the e2v and ST WS27C256L-12TMB variants are the same 32K x 8, 120 ns military CMOS EPROM, allowing procurement across multiple manufacturer codes without requalification when the form, fit, and function are preserved. The ceramic CLLCC package maintains compatibility with existing sockets and screening documentation. Buyers should demand traceability, verify date codes, and confirm the erasure window and marking authenticity, since obsolete military memory is a known target for counterfeit refurbished devices in the broker market.
Recomendado
Test Equipment Firmware Modules
Bench and ATE (automatic test equipment) systems from the military and industrial sectors frequently store instrument firmware in 27C256-family EPROMs, and the 27C256L-12TMB with its 120 ns access time and 32K x 8 organization is a common fit. Service organizations replacing failed firmware modules value the UV erasability: a unit can be read, verified against a golden image, corrected, and reprogrammed without consuming a fresh device. The 4.5 V to 5.5 V supply range tolerates aged instrument power supplies, and TTL-compatible tri-state outputs integrate directly into existing bus architectures. Keeping a programmer profile and image archive for each instrument model streamlines long-term support of these EOL-dependent systems.
Recomendado
Character Generator and Lookup Tables
Beyond code storage, the 27C256L-12TMB functions as a 32K-byte constant lookup table: waveform generators, video character generators, CRT display controllers, and math coprocessor adjuncts historically used EPROMs to store sine tables, font bitmaps, and state-machine transition tables. The 120 ns access time supports direct table addressing at video pixel rates for many legacy display formats, and the tri-state outputs allow the table ROM to share a bus with RAM. Because table contents never change in the field, the one-time programming model of an EPROM carries no practical penalty, making the EOL status of this device acceptable for these fixed-function roles in maintained systems.
Recomendado
Resumen de productos recomendados
Datos de referencia de ingeniería para 27C256L-12TMB — comparación, orientación de diseño e información de cumplimiento.
Guía de selección
Comparación con alternativas
| Parámetro | Este producto | WS27C256L-12TMB | WS27C256L-15TMB | 27C256A-12 | 27C256T-15/SO |
|---|---|---|---|---|---|
| Package | 28-pin CLLCC | 28-pin CLLCC - same | 28-pin CLLCC - same | 28-pin package - verify suffix | 28-pin ceramic - verify suffix |
| Brand | STMicroelectronics / WSI | STMicroelectronics | STMicroelectronics | STMicroelectronics | STMicroelectronics |
| Organization | 32K x 8 | 32K x 8 | 32K x 8 | 32K x 8 | 32K x 8 |
| Access Time | 120 ns | 120 ns | 150 ns | 120 ns | 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 |
| Memory Technology | CMOS UV EPROM | CMOS UV EPROM | CMOS UV EPROM | CMOS UV EPROM | CMOS UV EPROM |
| Lifecycle Status | EOL | EOL | EOL | EOL | EOL |
Diferenciadores clave
- Fastest military speed grade in family (frente a WS27C256L-15TMB)
- Multi-source military part number (frente a e2v 27C256L-12TMB)
- Ceramic military packaging (frente a 27C256T-15/SO commercial variants)
Notas de diseño
Never expose the erasure window to UV-opaque-unlabelled lighting: fluorescent lamps and direct sunlight contain UV wavelengths that will gradually corrupt stored data over months to years. Always cover the window with an opaque foil or qualified EPROM label after programming. Additionally, the VPP pin must be tied to VCC during read operation per the manufacturer datasheet; leaving VPP floating can cause undefined output states on this military CLLCC device.
For the 28-pin ceramic leadless chip carrier, define the PCB footprint from the datasheet CLCC package outline drawing, not from a generic PLCC-28 pattern, since military CLLCC land patterns differ in pad geometry and keep-out for the cavity window. Decouple VCC with a 0.1 uF ceramic capacitor placed within 10 mm of the package to suppress access-time glitches on the tri-state output bus during simultaneous address transitions.
The device operates from a 4.5 V to 5.5 V supply (minimum 4.5 V per Vyrian parametric data). During programming, the external programmer must supply the separate VPP voltage specified in the family datasheet - do not estimate this voltage, as over-voltage damages the cell array and under-voltage yields marginal program margins. Estimated: at CMOS static current levels (typically in the mA range for this family), power dissipation in read mode is a few tens of milliwatts, so no thermal design effort is normally required at 5 V.
Información de cumplimiento
Military ceramic-packaged EPROM predating modern compliance declarations; no RoHS/REACH status found in provided distributor data. Lead content in ceramic sealing glass is likely but unconfirmed.
