16 Mbit SPI Quad I/O flash — bus timing and page layout
The AT45DQ161-SSHF-T is a 16 Mbit non-volatile FLASH memory from Renesas, organised as 528 bytes × 4096 pages and accessed over a SPI bus with Quad I/O support at up to 85 MHz clock.
Page write timing and the firmware update budget
Word write cycle time is 8 µs typical; a full page write (528 bytes) completes in 6 ms typical. For a firmware image spanning 1024 pages, the total page-write time budgets roughly 6.1 seconds — the Quad I/O bus fills the page buffer faster than the write-while-erase cycle, so the bottleneck is the page program time, not the SPI clock. The 528-byte page size is non-standard for generic SPI NOR (which uses 256-byte pages) — the host controller's SPI driver must handle the larger buffer or pad partial-page writes. This is the same page layout as the AT45DB161E family, so code ported from that series needs no page-size workaround.
Package, supply rails, and board-fit checklist
The 85 MHz clock edge is fast enough that a 10 Ω series resistor at the SPI clock source damps reflections on traces longer than 50 mm.