27C256L-12TMB - 32Kx8 Military CMOS EPROM 120ns | WSI/ST
Référence : 27C256L-12TMB ✗ Fin de vie| Qté | Prix unitaire | 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 Présentation
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.
Alternatives de remplacement direct pour 27C256L-12TMB — 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 27C256L-12TMB (même facteur de forme et même empreinte) — différant par Package, Memory Type, Mounting Type, Memory Size, Organization.
Outil de comparaison rapide — sélectionnez des références alternatives pour une comparaison côte à côte :
WS27C256L-12TMB
✅ Remplacement direct📋 Alternative de référence (hors catalogue)
27C256L-12TMB
✅ Remplacement direct✓ En stock
$8.25 / unité
Voir la fiche technique →WS27C256L-15TMB
✅ Remplacement direct ⚠️ Spécifications non vérifiées📋 Alternative de référence (hors catalogue)
WS27C256L-12JI
✅ Remplacement direct ⚠️ Spécifications non vérifiées📋 Alternative de référence (hors catalogue)
27C256A-12
✅ Remplacement direct ⚠️ Spécifications non vérifiées✓ En stock
$2.52 / unité
Voir la fiche technique →27C256T-15/SO
✅ Remplacement direct ⚠️ Spécifications non vérifiées✓ En stock
$1.9 / unité
Voir la fiche technique →27C256L-12TMB Valeurs maximales et caractéristiques électriques
| Taille de mémoire | 256 Kbit |
| Organisation de la mémoire | 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 |
| Type de mémoire | UV EPROM |
| Temperature Grade | Military |
| Boîtier | 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 |
| Type de montage | Surface Mount |
| I/O Level | TTL compatible |
| Statut RoHS | unknown |
Configuration des broches de 27C256L-12TMB
| Broche 1 | A7 — Address input bit 7 |
| Broche 2 | A6 — Address input bit 6 |
| Broche 3 | A5 — Address input bit 5 |
| Broche 4 | A4 — Address input bit 4 |
| Broche 5 | A3 — Address input bit 3 |
| Broche 6 | A2 — Address input bit 2 |
| Broche 7 | A1 — Address input bit 1 |
| Broche 8 | A0 — Address input bit 0 |
| Broche 9 | Q0 — Data output bit 0 (tri-state) |
| Broche 10 | Q1 — Data output bit 1 (tri-state) |
| Broche 11 | Q2 — Data output bit 2 (tri-state) |
| Broche 12 | GND — Ground |
| Broche 13 | Q3 — Data output bit 3 (tri-state) |
| Broche 14 | Q4 — Data output bit 4 (tri-state) |
| Broche 15 | Q5 — Data output bit 5 (tri-state) |
| Broche 16 | Q6 — Data output bit 6 (tri-state) |
| Broche 17 | Q7 — Data output bit 7 (tri-state) |
| Broche 18 | CE — Chip enable |
| Broche 19 | A10 — Address input bit 10 |
| Broche 20 | OE — Output enable |
| Broche 21 | VPP — Programming voltage supply |
| Broche 22 | A8 — Address input bit 8 |
| Broche 23 | A9 — Address input bit 9 |
| Broche 24 | A11 — Address input bit 11 |
| Broche 25 | A12 — Address input bit 12 |
| Broche 26 | A13 — Address input bit 13 |
| Broche 27 | A14 — Address input bit 14 |
| Broche 28 | VCC — Power supply, 4.5 V to 5.5 V |
Applications typiques
27C256L-12TMB convient pour 6 applications: 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.
Recommandé
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.
Recommandé
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.
Recommandé
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.
Recommandé
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.
Recommandé
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.
Recommandé
Récapitulatif des produits recommandés
Données de référence d'ingénierie pour 27C256L-12TMB — comparaison, recommandations de conception et informations de conformité.
Guide de sélection
Comparaison avec les alternatives
| Paramètre | Ce produit | 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 |
Principaux différenciateurs
- Fastest military speed grade in family (vs WS27C256L-15TMB)
- Multi-source military part number (vs e2v 27C256L-12TMB)
- Ceramic military packaging (vs 27C256T-15/SO commercial variants)
Notes de conception
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.
Informations de conformité
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.
