32 Mbit SPI flash — page architecture and interface
The AT45DB321E-SHF-B is a 32 Mbit serial flash organized as 528 bytes × 8192 pages, accessed over an SPI bus at up to 85 MHz. The 528-byte page size is non-standard — most SPI NOR parts use 256-byte pages — so the firmware driver must account for the different sector mapping and erase granularity. The 2.3V–3.6V supply rail covers both 3.3V and 2.5V logic systems without a separate level translator on the SPI lines.
The supplier device package is listed as 8-SOIC — same mechanical outline, no exposed pad.
Write and erase timing — firmware update budget
Page write time is 8 µs typical; page erase takes 4 ms typical. For a firmware update of 256 KB, the erase latency dominates — roughly 2 seconds for the full chip if erased in page-sized chunks. The 85 MHz SPI clock keeps the read throughput high enough for execute-in-place (XIP) if the MCU supports it, but the 4 ms erase per page means the device is better suited for data logging or OTA staging than for frequent small-sector rewrites.