The R5F100FD is the 48 KB member of the 44-pin LQFP row: 3 KB of RAM, the 4
KB data flash, ten converter channels and forty I/O in the 10 by 10 mm body
at 0.8 mm pitch. It brings the 48 KB class’s FF300H self-RAM signature into
the family’s most fixture-friendly package, which makes it one of the
clearest members on which to study the family’s update machinery.

FF300H in the most readable package

The 48 KB class keeps its volatile memory at the top of the address space
from FF300H, and the flash library reserves its workspace right there. In
a recovered linker map the reservation is unambiguous, and on this member
every assertion in that map can be tested against the live chip through
0.8 mm leads without any packaging gymnastics, which is why the part
doubles as a reference for how the family’s update machinery is laid
out.

Forty-eight blocks, two clusters

The program occupies forty-eight erase blocks, and the update machinery
uses the bottom eight of them: four for the live boot region, four for
its mirror, with the security configuration duplicated at 010C0H and
010C4H and a flag in the first block choosing between the copies.
Field-updated boards keep both generations, the older one still holding
the firmware the unit carried out of the factory, and a capture reads
both as a matter of course.

Four-byte writes and where they stop

Writes land in four-byte words under per-block erase and verify, and
power lost mid-update leaves a half-converted word exactly where the
updater stopped. The package’s 0.8 mm leads make a full per-block
verification quick, so the signature is easy to find and easier to
interpret. Separating a failed update from a hardware fault is the first
fork in the job, and the second fork belongs to the chip reverse engineering service flow.

Ten channels and the control loop

The converter’s ten inputs cover the sensor spread of a control board,
their calibration in the 4 KB data flash and their thresholds in code.
The wear-levelled log beside them dates the unit’s working life. A
recovery takes both arrays and the option block together, because a
replacement controller that lacks the calibration regulates poorly and
one that lacks the option context starts up wrong.

Access and protection

The 0.8 mm leads make in-circuit fixtures and lifted-part work equally
simple, and the single-wire TOOL0 pad is usually routed. The protection
posture is family-standard: block protections enabled at shipment, the
debug gate and its erase bit in 000C3H, and both ten-byte identifiers in
block 0. The passive read of that block opens every job, exactly as it does
on the smallest members.

Row context

The 44-pin row runs from R5F100FA memory readout and R5F100FC locked flash through
R5F100FE program memory to R5F100FL firmware decryption. The same 48 KB class shows up in the
24-pin R5F1007D locked flash and 30-pin R5F100AD code flash extraction leaded parts, the
25-ball R5F1008D embedded memory and 36-ball R5F100CD firmware decryption grid parts, and the
40-pin QFN R5F100ED memory dump. Service entry points are firmware extraction service and
MCU crack service.

Three kilobytes and a streaming walker

The 48 KB class maps its volatile memory from FF300H and the flash
library reserves the top of the range, leaving just under a kilobyte
below for anything else. A readout walker fits: a small ring buffer,
serial transmit code and a block counter, nothing more. In return the
walker runs in circuit, keeps the application’s state untouched and
streams all forty-eight code blocks plus the 4 KB data array in one
pass. The four-byte programming word only matters on the write-back
side, but it is recorded in the session notes because a repair that
ignores it produces a board that fails on its next field update.

Budget arithmetic for the walker is settled in advance: buffer size, serial code, stack and a block counter must fit under the reservation with margin, and the linker places them explicitly rather than leaving it to defaults. A walker that fits is a walker that never disturbs the application, and on this class the discipline is verified by reading the counters and logs before and after the session and finding them identical.