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Microchip Technology AT28HC256-70PC
- Part No.:
- AT28HC256-70PC
- Manufacturer:
- Microchip Technology
- Category:
- Memory
- Package:
- 28-DIP (0.600", 15.24mm)
- Datasheet:
-
AT28HC256-70PC.pdf
- Description:
- IC EEPROM 256KBIT PARALLEL 28DIP
- Quantity:
- Payment:
- Shipping:
Inventory:3,342
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Product details
Overview
AT28HC256-70PC from Atmel is a 256 Kbit (32K × 8) parallel EEPROM with 70 ns read access time, JEDEC-standard byte-wide pinout, and single 5V ±10% supply. It supports automatic 64-byte page writes with internal latching and data polling for write completion detection, enabling reliable nonvolatile storage in embedded control and instrumentation systems.
For engineers reviewing the AT28HC256-70PC datasheet, AT28HC256-70PC pinout, AT28HC256-70PC application, or AT28HC256-70PC equivalent, key selection criteria include its 70 ns read timing, 3–10 ms page write cycle, hardware/software write protection, CMOS/TTL compatibility, and industrial temperature range support in PDIP packaging.
Technical Context
The AT28HC256-70PC operates as a drop-in parallel memory replacement for SRAM in legacy systems, requiring no external timing logic. Its internal address/data latches and control timer enable autonomous page programming of 1–64 bytes without host bus hold.
Write completion is verified via DATA Polling (I/O7 complement toggle) or Toggle Bit (I/O6 toggling), both usable at any point during the write cycle. Hardware protection includes VCC sense (<3.8 V inhibit), 5 ms power-on delay, and noise filtering on WE/CE inputs.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Memory Size | 256 Kbit (32,768 × 8), organized as byte-addressable parallel array |
| Read Access Time | 70 ns - enables direct interface with 14 MHz Z80, 8086, or 68000-based systems without wait states |
| Page Write Cycle | 3 ms (F-version) or 10 ms (standard) - determines minimum time between successive 64-byte updates |
| VCC Supply | 5 V ±10% - compatible with legacy TTL/CMOS logic rails; no auxiliary voltage required |
| Endurance | 10,000 write/erase cycles - sufficient for firmware patch storage or configuration logging in field-deployed equipment |
| Data Retention | 10 years at 85°C - validated for long-term unpowered storage in industrial environments |
| Operating Temperature | 0°C to +70°C (Commercial) - specified for stable operation in office and lab-grade electronics |
Pinout & Package
AT28HC256-70PC uses a 28-lead plastic dual in-line package (PDIP), 0.600" wide, with JEDEC-standard byte-wide pinout. Pin 1 is index-marked; pins 1 and 17 are not connected in PLCC variants but are valid address lines (A0, A1) in PDIP.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| A0–A14 | Address Inputs | 15-bit address bus supporting full 32K-word addressing; A0–A5 select bytes within 64-byte page during page write |
| CE | Chip Enable | Active-low chip select; must be low with OE low and WE high for read; inhibits writes when high |
| OE | Output Enable | Active-low output control; places I/O0–I/O7 in high-impedance state when high to prevent bus contention |
| WE | Write Enable | Active-low write strobe; falling edge latches address; rising edge latches data for byte or page write |
| I/O0–I/O7 | Bi-directional Data Bus | True bidirectional interface - drives data during write, presents stored data during read, high-Z during standby |
| VCC, GND | Power Supply | Single 5 V supply with <60 mA active current and <3 mA standby current - simplifies power design |
Key Features
| Feature | Design Value |
|---|---|
| Automatic Page Write | Internal 64-byte register allows burst loading of up to 64 bytes with single WE initiation - reduces host CPU overhead by >90% vs. byte-by-byte writes |
| DATA Polling | I/O7 returns complement of last written byte until write completes - enables deterministic polling without timers or interrupts |
| Hardware Write Protection | VCC sense, 5 ms power-on delay, and 15 ns noise filter on WE/CE - prevents spurious writes during power ramp or EMI events |
| Software Data Protection | Three-byte unlock sequence (AAh→55h→A0h) enables/disables write lock - protects critical configuration sectors without hardware modification |
| Extended Device ID | 64-byte dedicated EEPROM region (7FC0h–7FFFh) accessible via 12 V on A9 - supports unique device serialization or calibration data storage |
Applications
| Industrial PLC Configuration Storage | Legacy Computer BIOS/Firmware Patching |
|---|---|
Use Scenario: Storing runtime-modifiable ladder logic parameters and I/O mapping tables in programmable logic controllers operating in factory-floor environments. IC Role / Device Role / Timing Role: Nonvolatile configuration memory accessed via parallel bus during boot and runtime reconfiguration; 70 ns read ensures real-time parameter fetch without CPU stall. Use Value: Eliminates need for battery-backed SRAM; 10,000-cycle endurance supports daily firmware updates over 27 years; industrial temp rating (-40°C to +85°C) matches PLC thermal envelope. | Use Scenario: Field-upgradable BIOS patches and hardware initialization code in 1980s–1990s desktop PCs and workstations using ISA or VLB buses. IC Role / Device Role / Timing Role: Drop-in replacement for mask ROM or EPROM in socketed firmware slots; JEDEC pinout ensures PCB compatibility; 5 V-only operation avoids level-shifting. Use Value: Enables in-system reprogramming without UV eraser or socket removal; page write cuts update time from minutes (EPROM) to <10 ms per 64-byte sector. |
| Test Equipment Calibration Data Storage | Avionics Maintenance Log Buffer |
Use Scenario: Storing multi-point calibration coefficients and sensor offset corrections in benchtop multimeters and oscilloscopes requiring traceable metrology records. IC Role / Device Role / Timing Role: Dedicated nonvolatile memory bank accessed only during calibration mode; software data protection prevents accidental overwrite during normal measurement cycles. Use Value: 64-byte extended ID space stores serial number and calibration date; 10-year data retention meets ISO/IEC 17025 archival requirements without refresh. | Use Scenario: Recording flight-hour counters, fault codes, and maintenance timestamps in airborne navigation units where power loss is frequent and data integrity is safety-critical. IC Role / Device Role / Timing Role: Fault-tolerant event logger interfaced to microcontroller via parallel bus; hardware write protection ensures logs survive brownout conditions. Use Value: VCC-sense write inhibit prevents partial writes during voltage sag; toggle bit detection confirms write completion before next log entry - eliminates data corruption risk. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar parallel EEPROM applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| AT28C256-15PC | Slower 150 ns read access; same 256 Kbit density, 5 V supply, and PDIP package | Suitable for cost-sensitive, low-speed systems where 70 ns timing is unnecessary | Select when system clock <6.7 MHz eliminates need for fast access; retains identical pinout and software compatibility |
| MX28F256J3F-70PC | Intel-compatible 256 Kbit flash memory; requires 12 V for program/erase; no built-in page write logic | Used where block erase is acceptable and higher endurance (>100K cycles) is required | Choose only if existing firmware supports Intel flash command set; requires additional 12 V rail and erase management logic |
Compared with AT28HC256-70PC, AT28C256-15PC trades speed for cost in legacy systems, while MX28F256J3F-70PC shifts to flash architecture with higher endurance but adds voltage and command complexity - neither offers pin-compatible upgrade path without hardware or firmware revision.
Availability
AT28HC256-70PC is available at Aetrix Electronics and suitable for industrial control, legacy computing, test instrumentation, and avionics maintenance systems requiring stable component supply across extended product lifecycles.
Supply support for AT28HC256-70PC 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
Atmel Corporation (now part of Microchip Technology) is a semiconductor manufacturer specializing in microcontrollers, nonvolatile memory, and secure authentication ICs.
The AT28HC256 product line was designed for drop-in replacement of EPROM and battery-backed SRAM in industrial and computing systems requiring in-system reprogrammability without UV exposure or auxiliary power.
FAQ
What is the maximum page write size supported by the AT28HC256-70PC?
The AT28HC256-70PC supports a maximum page write size of 64 bytes. This is implemented via an internal 64-byte page register that latches address and data on the first write pulse, allowing up to 63 subsequent bytes to be loaded within 150 µs each. The AT28HC256-70PC enforces page boundaries using A6–A14; all bytes in a single page write must reside on the same 64-byte-aligned page.
Does the AT28HC256-70PC require a 12 V programming voltage?
No, the AT28HC256-70PC operates with a single 5 V ±10% supply for both read and write operations. A 12 V signal on A9 is required only for accessing the optional 64-byte device identification area (7FC0h–7FFFh); standard memory array reads and writes use 5 V exclusively. This eliminates need for charge pumps or auxiliary voltage regulators in most designs.
How does hardware write protection function on the AT28HC256-70PC?
Hardware write protection on the AT28HC256-70PC includes four mechanisms: (1) VCC sense circuitry inhibits writes if supply drops below ~3.8 V; (2) automatic 5 ms power-on delay after VCC stabilization; (3) write inhibition when CE is high, OE is low, or WE is high; and (4) 15 ns noise filter on WE and CE inputs. These features ensure the AT28HC256-70PC remains immune to spurious writes during power transitions or EMI events.
Can the AT28HC256-70PC be used as a direct replacement for standard SRAM in existing designs?
Yes, the AT28HC256-70PC is designed for SRAM-like read access - CE and OE low with WE high asserts data on I/O0–I/O7 within 70 ns, matching typical fast SRAM timing. However, write cycles require proper handshaking (DATA Polling or Toggle Bit) and are significantly slower than SRAM writes. The AT28HC256-70PC is ideal for read-heavy applications with infrequent writes, such as configuration storage or firmware patching.
What is the purpose of the extra 64 bytes of EEPROM in the AT28HC256-70PC?
The extra 64 bytes of EEPROM in the AT28HC256-70PC (address range 7FC0h–7FFFh) serve as a dedicated device identification area. Accessed by raising A9 to 12 V ±0.5 V, this region supports permanent storage of unique serial numbers, calibration constants, manufacturing dates, or firmware version stamps - independent of main memory array usage and protected from standard write commands.
AT28HC256-70PC Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Microchip Technology
- Series:
- -
- Package/Case:
- 28-DIP (0.600", 15.24mm)
- Packaging:
- Tube
- 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:
- 70 ns
- Voltage - Supply:
- 4.5V ~ 5.5V
- Operating Temperature:
- 0°C ~ 70°C (TC)
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Through Hole
- Supplier Device Package:
- 28-PDIP
AT28HC256-70PC FAQ
1.How can I place an order for AT28HC256-70PC through Aetrix?
Please submit a Request for Quotation (RFQ) for AT28HC256-70PC 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 AT28HC256-70PC reliable?
The price and inventory of AT28HC256-70PC are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for AT28HC256-70PC is usually 5 days.
3.What payment methods are accepted for AT28HC256-70PC?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for AT28HC256-70PC transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for AT28HC256-70PC?
AT28HC256-70PC orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your AT28HC256-70PC 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 AT28HC256-70PC?
For technical support, including AT28HC256-70PC datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your AT28HC256-70PC requirements.
6.How does Aetrix verify that AT28HC256-70PC is sourced from the original manufacturer or authorized distributors?
All AT28HC256-70PC 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 AT28HC256-70PC meets industry standards.
7.What is the process for return or replacement of AT28HC256-70PC?
All AT28HC256-70PC units undergo pre-shipment inspection (PSI). If there is an issue with AT28HC256-70PC, 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 AT28HC256-70PC part is unused and in its original packaging.
Return procedure for AT28HC256-70PC:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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