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Microchip Technology AT28HC256-90TU
- Part No.:
- AT28HC256-90TU
- Manufacturer:
- Microchip Technology
- Category:
- Memory
- Package:
- 28-TSSOP (0.465", 11.80mm Width)
- Datasheet:
-
AT28HC256-90TU.pdf
- Description:
- IC EEPROM 256KBIT PAR 28TSOP
- Quantity:
- Payment:
- Shipping:
Inventory:2,259
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Product details
Overview
AT28HC256-90TU from Microchip Technology is a military-grade 256-Kbit (32,768 × 8) paged parallel EEPROM with 90 ns read access time, 10 ms maximum page write cycle time, and full operation across –55°C to +125°C. It features internal 64-byte page latching, DATA Polling via I/O7, and hardware/software data protection - used in avionics control modules for nonvolatile configuration storage requiring radiation-tolerant, long-retention memory.
For engineers reviewing the AT28HC256-90TU datasheet, AT28HC256-90TU pinout, AT28HC256-90TU application, or AT28HC256-90TU equivalent, key selection criteria include military temperature compliance, JEDEC byte-wide pinout compatibility, page write timing (≤10 ms), VCC sense write inhibition, and toggle-bit end-of-write detection on I/O6.
Technical Context
The AT28HC256-90TU implements a static RAM-compatible parallel interface with dual-line chip enable (CE) and output enable (OE) control, enabling bus contention avoidance in multi-master systems. Its internal architecture includes a 64-byte page register, address/data latches, and an autonomous control timer that manages write completion without external strobes.
Write operations support byte and page modes: page writes accept 1–64 bytes within 150 µs per byte (tBLC), constrained to same-page addressing (A6–A14 fixed); DATA Polling (I/O7 complement) and Toggle Bit (I/O6 toggling) provide asynchronous write completion signaling independent of system clock.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Memory size | 256 Kbit (32,768 × 8) - supports full 16-bit address space with byte-level random access |
| Read access time | 90 ns - enables direct replacement of SRAM in legacy MIL-STD-1553B subsystems without timing redesign |
| Page write cycle time | Max 10 ms - allows burst programming of up to 64 bytes with single command initiation |
| Operating temperature | –55°C to +125°C - qualified for airborne vehicle flight control computers and missile guidance units |
| VCC supply | 5 V ±10% - compatible with legacy 5 V TTL/CMOS logic rails without level-shifting |
| Data retention | 10 years - ensures firmware integrity over full service life of deployed defense platforms |
| Endurance | 10,000 write cycles - sufficient for infrequent field-upgrade scenarios in mission-critical firmware storage |
| Write protection | Hardware VCC sense + software SDP (3-byte unlock sequence) - prevents corruption during power ramp-up/down in avionics power sequencing |
Pinout & Package
AT28HC256-90TU is supplied in a 32-lead CERDIP (Ceramic Dual Inline Package) with 0.600" width, MIL-STD-1835 D-10 Config A glass-sealed construction. Pin 1 is index corner; pins 1 and 17 are "Don't Connect" (DC) per CLCC variant but not present in CERDIP - CERDIP uses standard 28-pin layout with no DC pins.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| A0–A14 | Address inputs | 15-bit address bus supporting full 32K-word space; A6–A14 define page boundaries for 64-byte page writes |
| I/O0–I/O7 | Bidirectional data bus | CMOS/TTL-compatible 8-bit data path; I/O7 provides DATA Polling status, I/O6 provides Toggle Bit status |
| CE | Chip Enable | Active-low device select; must be low with OE low and WE high for read access; initiates write when falling edge coincides with address latch |
| OE | Output Enable | Active-low output gate; high-Z state when high, enabling shared bus operation without external tri-state logic |
| WE | Write Enable | Active-low write strobe; falling edge latches data; combined with CE controls byte vs. page write mode |
| VCC | Power supply | +5 V ±10% input; internal VCC sense circuit inhibits writes below ~3.8 V to prevent partial programming during brownout |
| GND | Ground reference | Signal and power return; decoupling capacitor required at package pin per MIL-HDBK-454A |
Key Features
| Feature | Design Value |
|---|---|
| JEDEC byte-wide pinout | Direct drop-in replacement for industry-standard 27C256 EPROMs and 62256 SRAMs in existing PCB layouts |
| Internal 64-byte page register | Eliminates need for external address/data latches during burst writes - reduces BOM count and board area in space-constrained modules |
| DATA Polling (I/O7) | Enables polling-based write completion detection without dedicated interrupt lines or timers - critical for resource-limited 8051-based avionics controllers |
| VCC sense write inhibit | Prevents spurious writes during power-up/down transients - eliminates need for external power-monitoring ICs in Class H/HV power domains |
| Software Data Protection (SDP) | 3-byte unlock sequence (AAh/55h/A0h) required before each protected write - prevents accidental reprogramming during field maintenance |
| Extra 64-byte ID sector | User-accessible memory block at 7FC0h–7FFFh (A9 = 12 V) for storing calibration data, serial numbers, or firmware version stamps |
Applications
| Avionics Flight Control Unit | Military Radio Firmware Storage |
|---|---|
Use Scenario: Storing real-time trim coefficients and sensor calibration tables updated only during ground maintenance. IC Role / Device Role / Timing Role: Nonvolatile configuration memory interfaced directly to a TMS320C31 DSP via parallel bus; accessed during boot and periodic self-test. Use Value: 10-year data retention and 10,000-cycle endurance ensure coefficient validity across 20+ year platform lifecycle without recalibration. | Use Scenario: Holding encrypted waveform definition tables and cryptographic keys in SINCGARS-compatible radios. IC Role / Device Role / Timing Role: Secure firmware repository with SDP enabled; accessed only by trusted bootloader during secure boot sequence. Use Value: Hardware VCC sense + SDP prevents key corruption during battery swap or voltage sag - maintaining FIPS 140-2 Level 2 compliance. |
| Tactical Vehicle Engine Control Module | Missile Guidance System Memory |
Use Scenario: Retaining engine mapping parameters and fault logs across extreme thermal cycling (-40°C to +85°C ambient, +125°C junction). IC Role / Device Role / Timing Role: Primary nonvolatile storage for ECU microcontroller (MC68332); read during startup, written after diagnostic sessions. Use Value: Full military temperature range operation eliminates derating and thermal margin calculations - reducing qualification test scope. | Use Scenario: Storing inertial navigation filter coefficients and mission-specific trajectory profiles in guided munitions. IC Role / Device Role / Timing Role: Radiation-hardened-by-process EEPROM interfaced to a rad-tolerant FPGA; programmed pre-launch and read-only in flight. Use Value: 90 ns read access meets tight timing budgets for real-time Kalman filter updates in high-G launch environments. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar EEPROM applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| AT28C256-90PU | Commercial grade (0°C to +70°C), same 90 ns access, identical pinout and command set | Lacks military temperature rating and VCC sense circuitry; not qualified for MIL-STD-883 testing | Select only for ground-based test equipment or non-mission-critical subsystems where cost drives decision |
| MX28F256J3F | 32-pin PLCC package, 120 ns access, 100,000-cycle endurance, Intel-compatible command set | Requires PCB redesign due to different footprint; slower access limits use in time-critical loops | Choose when higher endurance is mandatory and layout revision is feasible - e.g., depot-level reprogramming stations |
Compared with AT28C256-90PU, the AT28HC256-90TU adds military temperature range and VCC-sense write protection at the cost of higher unit price; versus MX28F256J3F, it offers faster access and drop-in CERDIP compatibility but lower endurance - making it optimal for field-deployed systems requiring guaranteed timing and rugged packaging.
Availability
AT28HC256-90TU is available at Aetrix Electronics and suitable for avionics flight control units, military radio firmware storage, and tactical vehicle engine control modules requiring stable component supply under extended temperature and long-life program commitments.
Supply support for AT28HC256-90TU includes scheduled delivery planning, volume procurement assistance, BOM continuity management, traceable sourcing, and lifecycle availability coordination for OEM customers, industrial embedded developers, connected-device designers, and electronics production programs.
Manufacturer
Microchip Technology is a U.S.-based semiconductor company specializing in microcontrollers, analog devices, and nonvolatile memory solutions for industrial, automotive, and aerospace markets.
The AT28HC256 belongs to Microchip's high-reliability parallel EEPROM product line, designed specifically for military and aerospace applications demanding extended temperature operation, long data retention, and robust write protection against power anomalies.
FAQ
What is the maximum page write cycle time for AT28HC256-90TU?
The AT28HC256-90TU has a maximum page write cycle time of 10 ms, as specified in the DS20006352A datasheet Table 6-4. This applies to the standard endurance grade (10,000 cycles); the "F" variant supports 3 ms but is not applicable to the -90TU suffix. The 10 ms value governs worst-case timing for full 64-byte page writes under military temperature extremes.
Does AT28HC256-90TU support both hardware and software write protection?
Yes, AT28HC256-90TU implements dual-layer write protection: hardware-level VCC sensing (inhibits writes below ~3.8 V) and noise filtering on WE/CE inputs, plus software Data Protection (SDP) activated via a three-byte unlock sequence (AAh/55h/A0h). Both mechanisms operate concurrently and are documented in Section 6.11 of the DS20006352A datasheet.
Which pins are designated "Don't Connect" on AT28HC256-90TU?
The AT28HC256-90TU in 32-lead CERDIP package has no "Don't Connect" pins - the DC designation applies only to the 32-lead CLCC variant (pins 1 and 17). Per DS20006352A-page 4 Table 2-1 and page 21 package drawing, the CERDIP uses all 28 signal pins; NC entries in the pin table refer to unused positions in alternate packages, not the -90TU CERDIP.
Can AT28HC256-90TU be used as a direct replacement for 27C256 EPROMs?
No, AT28HC256-90TU is not a pin-compatible or functional replacement for 27C256 EPROMs. While it shares JEDEC byte-wide pinout, it requires active VCC during writes (unlike UV-erasable EPROMs), uses different write enable timing, and lacks UV window. It replaces 27C256 only in systems redesigned to support EEPROM write protocols and power sequencing - not hot-swap.
What is the purpose of the extra 64-byte memory sector in AT28HC256-90TU?
The extra 64-byte sector (addresses 7FC0h–7FFFh) in AT28HC256-90TU is user-programmable EEPROM space accessible only when A9 is raised to 12.0 V ±0.5 V. It is intended for device identification, calibration data storage, or firmware version tracking - separate from main array to avoid interference during normal operation, as defined in Section 6 of DS20006352A.
AT28HC256-90TU Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Microchip Technology
- Series:
- -
- Package/Case:
- 28-TSSOP (0.465", 11.80mm Width)
- Packaging:
- Tray
- Product Status:
- Obsolete
- Programmable:
- Not Verified
- Memory Type:
- Non-Volatile
- Memory Format:
- EEPROM
- Technology:
- EEPROM
- Memory Size:
- 256Kbit
- Memory Organization:
- 32K x 8
- Memory Interface:
- Parallel
- Clock Frequency:
- -
- Write Cycle Time - Word, Page:
- 10ms
- Access Time:
- 90 ns
- Voltage - Supply:
- 4.5V ~ 5.5V
- Operating Temperature:
- -40°C ~ 85°C (TC)
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- 28-TSOP
AT28HC256-90TU FAQ
1.How can I place an order for AT28HC256-90TU through Aetrix?
Please submit a Request for Quotation (RFQ) for AT28HC256-90TU on Aetrix. Our sales agent will provide a competitive quotation and guide you through the order confirmation once you accept the terms.
2.Are the price and stock information for AT28HC256-90TU reliable?
The price and inventory of AT28HC256-90TU are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for AT28HC256-90TU is usually 5 days.
3.What payment methods are accepted for AT28HC256-90TU?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for AT28HC256-90TU transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for AT28HC256-90TU?
AT28HC256-90TU orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your AT28HC256-90TU order is processed, you will receive an email with the shipment details and tracking number.
Note: Tracking information may take up to 24 hours to appear. Express delivery typically takes 3–5 business days.
5.How can I obtain technical support or documentation for AT28HC256-90TU?
For technical support, including AT28HC256-90TU datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your AT28HC256-90TU requirements.
6.How does Aetrix verify that AT28HC256-90TU is sourced from the original manufacturer or authorized distributors?
All AT28HC256-90TU products on Aetrix are procured from qualified distributors and authorized channels. Our dedicated quality assurance team conducts strict verification, including traceability checks and, if necessary, third-party testing. This ensures that AT28HC256-90TU meets industry standards.
7.What is the process for return or replacement of AT28HC256-90TU?
All AT28HC256-90TU units undergo pre-shipment inspection (PSI). If there is an issue with AT28HC256-90TU, returns or replacements are accepted under the following conditions:
1.Quantity discrepancies, incorrect items, or visible external defects (such as breakage or corrosion), acknowledged by Aetrix.
2.The issue is reported within 90 days of delivery.
3.The AT28HC256-90TU part is unused and in its original packaging.
Return procedure for AT28HC256-90TU:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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