AT45DB321E-SHF-T

The AT45DB321E-SHF-T is a 32Mbit (4M x 8) DataFlash serial Flash memory from Renesas Electronics (formerly Adesto Technology), housed in an 8-pin SOIC 208-mil package. The device belongs to the System Enhancing class of code and data storage solutions, distinguished by its advanced dual SRAM buffer architecture that makes it the most efficient memory for data logging applications.

The AT45DB321E features two independent SRAM data buffers (each 256 or 264 bytes depending on page size mode) that enable simultaneous read-while-write operations: while data is being programmed from one buffer to the main memory, new data can be loaded into the other buffer. This dual-buffer architecture eliminates the programming wait time that single-buffer Flash memories require, dramatically improving data throughput in continuous logging applications.

The memory supports two page size configurations: standard DataFlash page size of 528 bytes (528 x 8,192 pages = 32,030,208 bits + 1,048,576 extra bits) and binary page size of 512 bytes (512 x 8,192 pages = 33,554,432 bits). The page erase granularity of 256 bytes (half-page) is the smallest erase unit available in any serial Flash, providing maximum flexibility for data logging applications where small data records must be updated frequently without erasing large sectors.

The SPI interface supports Mode 0 (CPOL=0, CPHA=0) and Mode 3 (CPOL=1, CPHA=1) at clock frequencies up to 85MHz. The device uses a 4-wire SPI interface: CS (chip select), SCK (serial clock), SI (serial input), and SO (serial output). The WP (write protect) pin provides hardware sector protection, and the RESET pin allows external reset of the internal state machine.

Additional features include: byte-write capability (enabling serial EEPROM-like random byte access), ultra-deep power-down mode (0.4uA typical), comprehensive security features (sector lockdown, write protection, unique 64-bit device ID, security register), and RapidS protocol for high-speed continuous read operations. The device is guaranteed for 100,000 page erase/program cycles per page with 20-year data retention. Renesas guarantees product longevity to 2034.

The SHF suffix denotes: S = SOIC-8 package, H = industrial temperature grade with NiPdAu lead finish, F = 2.3V minimum operating voltage. The T suffix denotes tape and reel packaging (2,250 units per reel). The device is RoHS3 compliant, MSL Level 1, and classified as ECCN 3A991B1A.

The AT45DB321E-SHF-T operates as a page-erase DataFlash serial memory with a dual SRAM buffer architecture, controlled through SPI command sequences from a host microcontroller.

Dual SRAM Buffer Architecture: The key differentiator of the AT45DB321E is its two independent SRAM data buffers (Buffer 1 and Buffer 2), each matching the page size (528 or 512 bytes). These buffers serve as intermediate holding areas between the SPI interface and the main Flash memory array. Data is first written from the SPI bus into a buffer, then programmed from the buffer to the main memory page. This architecture enables three critical capabilities: (1) Read-while-write: while data from Buffer 1 is being programmed into a main memory page, the host can simultaneously read data from Buffer 2 or from a different main memory page; (2) Continuous data logging: new sensor data fills Buffer 2 while Buffer 1 is being programmed, eliminating dead time between measurements; (3) Compare-then-program: data in a buffer can be compared with a main memory page before programming to verify data integrity.

Page Erase and Program: Unlike standard SPI Flash memories that erase in 4KB sectors minimum, the AT45DB321E supports page-level erase (256 or 264 bytes minimum) and even byte-level write within a page. The smallest erase granularity makes it ideal for data logging where small records are updated frequently. The page program time is typically 4ms, and the page erase time is typically 35ms.

SPI Command Protocol: The host communicates by asserting CS LOW, clocking in an 8-bit opcode on SI, followed by address bytes and data as required by the command. Over 40 opcodes support operations including: continuous array read (1Bh for high-frequency mode up to 85MHz), buffer read/write (84h/82h for Buffer 1, 85h/83h for Buffer 2), buffer-to-main-memory program with erase (83h/86h), buffer-to-main-memory program without erase (88h/89h), main-memory-page-to-buffer transfer (53h/55h), main-memory-page-to-buffer compare (60h/61h), auto page rewrite (58h/59h), status register read (D7h), and manufacturer/device ID read (9Fh).

Status Register: The 8-bit status register (read via opcode D7h) provides critical operational status: Bit 7 (RDY/BUSY) indicates whether the device is ready for a new command (1=ready, 0=busy), Bit 6 (COMP) indicates the result of a buffer-to-main-memory compare operation (1=mismatch, 0=match), and Bits 0-1 indicate the page size configuration and sector protection status.

Write Protection: The WP pin provides hardware write protection for sectors configured as protected via the Sector Protection Register. When WP is asserted LOW, any program or erase command to a protected sector is ignored. Sector protection is configured through a separate command sequence and can be permanently locked via the Sector Lockdown command, preventing any future modification. This provides defense-in-depth against accidental or malicious data corruption.

Ultra-Deep Power-Down: The ultra-deep power-down command (79h) reduces current consumption to 0.4uA (typical), significantly lower than the standard deep power-down mode. Exit from ultra-deep power-down requires a dedicated wake command followed by a recovery time. This mode is useful for battery-powered data loggers that spend most of their time in sleep mode between measurement intervals.