R5F100EH tops the 40-pin row at 192 KB of code flash with 16 KB of RAM, the
8 KB data flash and nine converter channels in the 6 by 6 mm HWQFN. It is
the largest program store the family offers at this pin count, and the
capacity where the RL78 core’s segmented addressing, the boot-swap update
zone and a substantial data array all operate together in a package that
still fits a thumbnail.

One hundred ninety-two blocks of segmented image

One hundred ninety-two erase blocks carry the program, the lowest four
holding the boot region and the next four its mirror. Above them the
application is banked: the compiler reaches past the core’s 64 KB window
through the segment register, and at 192 KB it leans on that throughout.
A reconstruction that ignores the banking yields a binary that will not
run, so the disassembly that guides any repair carries window context
from the first block to the last.

Sixteen KB of RAM and the working set

Sixteen kilobytes give the image room for the flash library, a
field-update protocol and communication buffers to sit beside the
control law, and the reservation the library makes at the top of that
space shows in any linker map recovered from the part. Boards of this
capacity are updated in the field as a matter of course, so both boot
copies are usually written and a byte in the first block names the one
the reset logic trusts. The copy left behind keeps the firmware the
product carried before its first update, and reading it turns a repair
into a history lesson.

The 8 KB data flash as the unit’s record

At this capacity the separate data array is the 8 KB version, and
firmware-fault histories, calibration generations and usage logs live
there. It is read with the data-flash command set and captured with its own
protection flags, and the wear-levelled records inside it date the unit’s
service life in a form that survives disputes. Code without the array is
half a recovery on this member.

Protection and the first move

Everything that decides how closed the chip is sits inside its first
kilobyte: four configuration bytes covering watchdog, detector and
oscillator policy, the fourth of which also gates debugging and carries
the choice to wipe the array when a comparison fails; and the two
ten-byte identifiers, one asked for by an emulator, the other by the
programmer on the serial wire. The serial one is almost always present
on boards of this size. Reading that kilobyte through the idle read
path, before any tool is attached, sets the plan for everything that
follows, and the shield window, where firmware confines its own
updates, is noted with the same capture.

The QFN and the fan-in

Forty pins at 0.5 mm pitch with a bonded centre pad leave fixture room on
the wings, and production layouts usually route the single-wire TOOL0 pad.
Where nothing is exposed, lift-and-reball onto an adapter is routine. The
die itself remains reachable through the IC decapsulation service route, and the
examination-level work is the chip reverse engineering service flow.

Row context

The 40-pin siblings are in R5F100EA program memory through R5F100EG code flash extraction. The same
capacity in larger packages is the 44-pin R5F100FH flash data and the 48-pin
R5F100GH flash data; in the QFN rows below it is the 32-pin class up to
R5F100BG flash data. For the boot-swap mechanics that the update zone relies on,
the dedicated note is R5F100FE boot cluster recovery, and the family service entry is
the MCU crack service page.

Three windows of application code

One hundred ninety-two erase blocks hold the program, the application
occupying three 64 KB windows above the boot region and its mirror. At
this capacity the inactive boot copy is not the only historical layer:
protocol modules and string tables accumulate across the banked windows,
and a diff between the two boot copies usually names the modules that
changed while leaving the banked library untouched. The doubled data
store carries the run history, and the ten converter inputs carry the
sensing plan, so a complete capture documents the unit from three
directions at once and cross-checks itself.

The identification of module boundaries follows the same evidence: revision stamps inside the banked tables, string growth across generations and driver code that persists while the application around it moves. For a rebuild, those boundaries are the natural seams, and respecting them keeps a patched image consistent with its own update machinery.