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Microchip Technology AT28HC256-70JU-T
- Part No.:
- AT28HC256-70JU-T
- Manufacturer:
- Microchip Technology
- Category:
- Memory
- Package:
- 32-LCC (J-Lead)
- Datasheet:
-
AT28HC256-70JU-T.pdf
- Description:
- IC EEPROM 256KBIT PAR 32PLCC
- Quantity:
- Payment:
- Shipping:
Inventory:1,783
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Product details
Overview
AT28HC256-70JU-T from Microchip Technology is a 256-Kbit (32,768 × 8) parallel EEPROM with 70 ns read access time, single 5V ±10% supply operation, JEDEC-approved byte-wide pinout, and industrial temperature range (–40°C to +85°C). It supports automatic page write of up to 64 bytes, hardware/software data protection, and DATA Polling for write completion detection - deployed in embedded control firmware storage, industrial PLC configuration memory, and legacy ISA-bus peripheral BIOS retention.
For engineers reviewing the AT28HC256-70JU-T datasheet, AT28HC256-70JU-T pinout, AT28HC256-70JU-T application, or AT28HC256-70JU-T equivalent, key selection considerations include its 70 ns read timing, PLCC-32 package compatibility with legacy socketed designs, 10,000/100,000 write endurance rating, and dual hardware/software write protection mechanisms for field-deployed systems.
Technical Context
The AT28HC256-70JU-T implements a static RAM-compatible parallel interface with CE/OE/WE three-line control logic, enabling direct drop-in replacement in SRAM-based address/data bus architectures. Its internal 64-byte page register latches sequential writes without external timing control, and the device uses VCC-sense and noise-filtered WE/CE inputs to prevent spurious programming during power transients.
Write completion is confirmed via I/O7 DATA Polling (complement-to-data toggle) or I/O6 Toggle Bit behavior - both usable at any point during tWC (≤10 ms). The device includes 64 bytes of dedicated identification memory accessible at 7FC0H–7FFFH using A9 = 12V, and optional software chip erase via 6-byte command sequence.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Memory Size | 256 Kbit (32,768 × 8), directly addressable as byte-wide parallel memory |
| Read Access Time | 70 ns max - enables direct substitution for fast SRAM in legacy 8-bit/16-bit microcontroller systems |
| Page Write Cycle | ≤10 ms max - supports burst programming of up to 64 contiguous bytes per internal cycle |
| Endurance | 10,000 or 100,000 write/erase cycles - selectable variant-dependent; JU-T denotes standard 10k rating |
| Data Retention | 10 years at +85°C - validated for long-life industrial deployments without refresh |
| Supply Voltage | 5V ±10% - operates from standard TTL/CMOS logic rails without auxiliary regulators |
| Operating Temperature | –40°C to +85°C - qualified for industrial-grade PCB environments |
| Power Dissipation | 440 mW active (80 mA @ 5V), <3 mA standby - reduces thermal load in dense control modules |
Pinout & Package
AT28HC256-70JU-T is packaged in a 32-lead Plastic Leaded Chip Carrier (PLCC) with gull-wing leads, RoHS-compliant green molding compound, and JEDEC-standard footprint. Pin 1 is indexed by corner chamfer; pins 1 and 17 are "Don't Connect" (DC) and must remain unconnected per datasheet.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| A0–A14 | Address Inputs | 15-bit address bus (A0 LSB to A14 MSB); A6–A14 define 64-byte page boundaries for page write |
| I/O0–I/O7 | Bidirectional Data Bus | 8-bit parallel data path; I/O7 used for DATA Polling, I/O6 for Toggle Bit status indication |
| CE | Chip Enable | Active-low chip select; must be low with OE low and WE high for read; initiates write when pulsed low with OE high |
| OE | Output Enable | Active-low output gate; controls bus drive; high during write, low during read |
| WE | Write Enable | Active-low write strobe; falling edge latches address/data; high during read |
| VCC | Power Supply | +5V ±10% main supply; internal VCC-sense circuit inhibits writes below ~3.8V |
| GND | Ground Reference | Signal and power return; pin 16 on PLCC; requires low-impedance PCB plane |
| NC / DC | No Connect / Don't Connect | Pins 12 and 26 are NC; pins 1 and 17 are DC - must float, not tied to VCC/GND |
Key Features
| Feature | Design Value |
|---|---|
| JEDEC byte-wide pinout | Enables direct PCB-level replacement of obsolete 27C256 EPROMs and 62256 SRAMs without layout change |
| Hardware write protection | VCC-sense, 5 ms power-on delay, and 15 ns noise filtering prevent accidental writes during brown-out or EMI events |
| Software data protection (SDP) | Three-step 5555H/2AAAH/A0H command sequence enables/disables full-device write lock - persistent across power cycles |
| 64-byte page register | Reduces system bus occupancy during multi-byte writes; allows host CPU to perform other tasks while internal timer executes programming |
| Identification memory | 64 bytes at 7FC0H–7FFFH, accessible with A9 = 12V, support unique device serialization and calibration data storage |
| DATA Polling & Toggle Bit | Dual asynchronous write-complete detection methods eliminate need for fixed delay timers or external status polling hardware |
Applications
| Industrial Control Firmware Storage | Legacy ISA-Bus Peripheral BIOS |
|---|---|
|
Use Scenario: Storing configuration parameters and firmware patches for programmable logic controllers (PLCs) operating in factory-floor environments with wide temperature swings and electrical noise. IC Role / Device Role / Timing Role: Nonvolatile program memory mapped into microcontroller address space; accessed via parallel bus with 70 ns read latency to meet real-time scan-cycle deadlines. Use Value: 10-year data retention and 10,000-cycle endurance ensure firmware integrity over equipment lifetime without battery backup or refresh routines. |
Use Scenario: Holding BIOS initialization code and hardware configuration tables for ISA expansion cards (e.g., data acquisition, motion control) in retro-computing and industrial PC systems. IC Role / Device Role / Timing Role: Byte-addressable ROM replacement; emulates 27C256 EPROM timing but supports in-system reprogramming without UV erasure or socket removal. Use Value: JEDEC pinout and 5V-only operation allow direct socket replacement; page write cuts field update time vs. byte-by-byte programming. |
| Embedded System Configuration Memory | Medical Device Calibration Storage |
|
Use Scenario: Retaining user-adjusted operational settings (e.g., alarm thresholds, sampling rates) in portable diagnostic instruments subject to frequent power cycling. IC Role / Device Role / Timing Role: Standalone configuration EEPROM interfaced to an 8-bit MCU; accessed only during boot or menu navigation - low 3 mA standby current extends battery life. Use Value: Hardware + software write protection prevents corruption during unexpected shutdowns; DATA Polling ensures reliable parameter save confirmation. |
Use Scenario: Storing factory-calibrated sensor offset/gain coefficients and regulatory compliance metadata in Class II medical devices requiring traceable, tamper-resistant memory. IC Role / Device Role / Timing Role: Secure nonvolatile storage with 64-byte ID area used for calibration certificate hash and manufacturing lot traceability (7FC0H–7FFFH). Use Value: 12V-programmable ID region enables post-manufacturing calibration write under controlled conditions; 100,000-cycle endurance supports recalibration service intervals. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar parallel EEPROM applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| AT28HC256-90JU-T | Slower 90 ns read access time; otherwise identical pinout, timing, and feature set | Suitable where system timing budget permits relaxed read latency; lower cost in volume | Select when 70 ns speed margin is unnecessary and BOM cost optimization is prioritized |
| AT28HC256-70PU | Same 70 ns speed but in 28-pin SOIC package (vs. 32-pin PLCC); different pin mapping and smaller footprint | Used in new designs with space-constrained PCBs; not socket-compatible with PLCC-based legacy boards | Choose for compact modern layouts; avoid for drop-in replacement of PLCC-socketed AT28HC256-70JU-T |
Compared with AT28HC256-70JU-T, the -90JU-T trades 20 ns read speed for cost savings without altering system integration, while the -70PU offers identical performance in a smaller SOIC package - requiring PCB redesign but enabling higher board density.
Availability
AT28HC256-70JU-T is available at Aetrix Electronics and suitable for industrial control firmware storage, legacy ISA-bus peripheral BIOS updates, and embedded system configuration memory requiring stable component supply across extended product lifecycles.
Supply support for AT28HC256-70JU-T 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 global semiconductor company specializing in microcontrollers, analog components, and nonvolatile memory solutions, with a focus on industrial, automotive, and aerospace reliability standards.
The AT28HC256 product line delivers high-speed, pin-compatible EEPROMs designed for seamless migration from EPROM and battery-backed SRAM in legacy computing and control systems.
FAQ
What is the maximum write endurance rating for the AT28HC256-70JU-T?
The AT28HC256-70JU-T is rated for 10,000 write/erase cycles under standard conditions. A variant marked with 'E' suffix (e.g., AT28HC256-70JU-TE) provides extended 100,000-cycle endurance. Endurance is verified per JEDEC standard JESD22-A117 and applies to the full memory array including the 64-byte ID region. The AT28HC256-70JU-T datasheet specifies this value in Section 4.3 DC Characteristics and Table 6-4 Page Mode Write Characteristics.
Does the AT28HC256-70JU-T require a 12V supply for normal operation?
No, the AT28HC256-70JU-T operates from a single 5V ±10% supply for all standard read/write functions. A 12V ±0.5V supply is required only for accessing the 64-byte device identification memory (addresses 7FC0H–7FFFH), which is done by raising A9 to 12V. This high-voltage mode is strictly for factory programming or calibration and is not used during routine operation of the AT28HC256-70JU-T.
How does DATA Polling work on the AT28HC256-70JU-T?
During a write cycle, reading the last written byte from the AT28HC256-70JU-T returns the bitwise complement of that data on I/O7. When the write completes, true data appears on I/O7 and all other I/O lines. This allows the host processor to poll I/O7 in a loop without fixed delays - eliminating timing uncertainty. The AT28HC256-70JU-T supports this method per Section 6.14 Data Polling Characteristics and Figure 6-15 waveform.
Can the AT28HC256-70JU-T be used as a direct replacement for a 27C256 EPROM?
Yes, the AT28HC256-70JU-T uses the same JEDEC-standard 32-pin PLCC footprint and byte-wide pinout as the 27C256, enabling socket-level replacement. However, unlike UV-erasable EPROMs, the AT28HC256-70JU-T supports in-system electrical erasure and programming. No hardware changes are needed beyond ensuring the 5V supply meets ±10% tolerance and that WE/OE/CE control logic complies with AT28HC256-70JU-T timing (tWP ≥100 ns, tAS ≥0 ns).
What is the purpose of pins 1 and 17 on the AT28HC256-70JU-T PLCC package?
Pins 1 and 17 on the AT28HC256-70JU-T are designated "Don't Connect" (DC) per Microchip's DS20006428B datasheet Section 2 Pin Descriptions and Package Drawing C04-023. These pins must remain electrically floating - they are not bonded internally and must not be tied to VCC, GND, or any signal. Connecting them risks undefined behavior or damage. This requirement is explicitly called out in the AT28HC256-70JU-T pin function table and package marking documentation.
AT28HC256-70JU-T Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Microchip Technology
- Series:
- -
- Package/Case:
- 32-LCC (J-Lead)
- Packaging:
- Tape & Reel (TR)
- Product Status:
- Active
- 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:
- 70 ns
- Voltage - Supply:
- 4.5V ~ 5.5V
- Operating Temperature:
- -40°C ~ 85°C (TC)
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- 32-PLCC (11.43x13.97)
AT28HC256-70JU-T FAQ
1.How can I place an order for AT28HC256-70JU-T through Aetrix?
Please submit a Request for Quotation (RFQ) for AT28HC256-70JU-T 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 AT28HC256-70JU-T reliable?
The price and inventory of AT28HC256-70JU-T are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for AT28HC256-70JU-T is usually 5 days.
3.What payment methods are accepted for AT28HC256-70JU-T?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for AT28HC256-70JU-T transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for AT28HC256-70JU-T?
AT28HC256-70JU-T orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your AT28HC256-70JU-T 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 AT28HC256-70JU-T?
For technical support, including AT28HC256-70JU-T datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your AT28HC256-70JU-T requirements.
6.How does Aetrix verify that AT28HC256-70JU-T is sourced from the original manufacturer or authorized distributors?
All AT28HC256-70JU-T 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 AT28HC256-70JU-T meets industry standards.
7.What is the process for return or replacement of AT28HC256-70JU-T?
All AT28HC256-70JU-T units undergo pre-shipment inspection (PSI). If there is an issue with AT28HC256-70JU-T, 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 AT28HC256-70JU-T part is unused and in its original packaging.
Return procedure for AT28HC256-70JU-T:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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