R5F100FK is the 384 KB member of the 44-pin LQFP row: 24 KB of RAM, the 8 KB
data flash, ten converter channels and forty I/O in the 10 by 10 mm body at
0.8 mm pitch. It sits one step below the family’s largest member and shares
every structural feature with it: a segmented image, a two-cluster update
zone, an 8 KB data array and the protection architecture that ships enabled
on every part of the line.

Three hundred eighty-four blocks

Three hundred eighty-four erase blocks make up the program store, four
at the bottom for the boot region and four more for its mirror.
Verification across that many blocks is a manifest discipline: each
kilobyte checksummed, drift between sessions investigated, and only a
clean manifest accepted. The capture itself streams through 0.8 mm leads
in seconds, which is why the leaded members of this capacity are the
preferred study subjects for the large-memory class.

Twenty-four KB of RAM and the segmented image

Twenty-four kilobytes host the library, the updater and a real
communication stack beside the application, and the reservation in the
linker map marks the build as update-capable. The image above the flash
is banked across the core’s windows, and a rebuild that keeps those
assignments runs where a flattened one will not. Both boot copies are
written on maintained boards, and the flag byte in the first block says
which one the reset logic chose last.

The update zone and the previous generation

The two clusters at the bottom of the array carry their own option bytes
and identifiers, duplicated at 010C0H and 010C4H, and the flag that
chooses between them lives in the first erase block. Boards maintained
over years accumulate a visible sequence: each update rewrites one
cluster, flips the flag, and leaves the previous generation intact next
door. Walked in order, the copies and the wear counters in the data
array reconstruct the whole maintenance record without a single
document.

The doubled data array

The 8 KB store carries fault histories, calibration revisions and usage
counters under wear levelling, read with its own command set and its own
flags. On industrial boards at this capacity it is the unit’s biography,
and a rebuild that skips it leaves the controller with instructions and
no memory of what it regulates.

Protection and the first move

Everything gateable is gated from the first kilobyte: the four option
bytes, the debug decision and its wipe-on-failure choice, and the two
ten-byte secrets, one for each programming tool. Block protections ship
enabled and the shield window, common at this capacity, is captured with
the rest. The passive first read of that kilobyte is what every job here
starts from.

Access and the bench

At 0.8 mm nothing physical gets in the way: fixtures, adapters and
lifts are routine, and the part returns to its socket fit for service.
The IC decapsulation service route, the firmware extraction service page and the chip reverse engineering service flow cover
the escalation steps in that order.

Row context

The 44-pin siblings are in R5F100FA memory readout through R5F100FJ flash memory and
R5F100FL firmware decryption. The 384 KB die in the 48-pin package is R5F100GK code flash extraction.
For the top of the row, the 512 KB member is R5F100FL firmware decryption, and the
family-level service index is microcontroller unlock.

One manifest for three hundred eighty-four blocks

At this capacity the deliverable of a capture session is as much the
manifest as the dump: three hundred eighty-four block checksums, the
option-byte state, the boot flag, the data-array flags and the six
segment assignments, all cross-referenced in one document. The manifest
is what makes a write-back provable and what makes a second session,
months later, comparable with the first. Any block whose checksum
drifted between sessions is re-read before conclusions are drawn from
it, and drift itself is information, since firmware at this capacity
rarely rewrites the upper windows.

The same manifest drives the repair side. Patched code is placed by
segment, verified per block against the manifest, and only then
released to the boot machinery that will swap it in. Six windows of
banked code assemble without guesswork, which is the quiet difference
between a rebuild that works and one that merely assembles.

Volatile memory at 24 KB removes the usual constraint on session
tooling: buffers can be generous, the library and the application
coexist, and the capture finishes with the board’s counters
undisturbed. The 44-pin body keeps the physical work ordinary
throughout.