R5F100GJ is the 256 KB member of the 48-pin row: 20 KB of RAM, the 8 KB
data flash, ten converter channels and forty-four I/O in the 7 by 7 mm
LFQFP at 0.5 mm pitch. At two hundred fifty-six blocks the code array
crosses the byte-boundary in block numbering, the image above it is
segmented throughout, and the package gives the wide I/O spread that
boards of this capacity are built around.

Two hundred fifty-six blocks under 0.5 mm leads

The program store spans two hundred fifty-six erase blocks, the bottom
four reserved for the boot region and the next four for its mirror. A
capture verifies each kilobyte as it streams, so contact problems cost
one block rather than the image. Block numbering here exactly fills an
eight-bit index, a detail the current library handles with wider
integers and older 8-bit-era tooling does not, which makes custom
scripts written for smaller members fail first at exactly this count.

Twenty KB of RAM and the segmented image

The volatile memory carries a communication stack, a logging engine and
the flash library at the same time, and the space it reserves at the top
flags an update-capable build in any recovered map. The banked layout
above the flash is carried through every rebuild, and maintained boards
keep both boot copies on disk with the first block’s flag naming the
live one.

The update zone and the field history

Each cluster at the bottom of the array holds its own copy of the
security bytes at 010C0H and 010C4H, and the flag in the first
block chooses between them. Maintained boards show the sequence plainly:
rewrite one cluster, invert the flag, leave the previous generation
standing next door. The wear counters in the data array date each step,
and a capture that reads only one cluster throws away half the
evidence.

The data array as memory

Under wear levelling the separate store accumulates fault histories,
calibration revisions and usage counters, fetched with its own command
set behind flags of its own. On the industrial boards this member
serves, the array is the unit’s memory, and a rebuilt controller without
it knows its instructions but not its history.

Protection and the first move

Four option bytes cover watchdog, detector and oscillator policy, the
fourth doubles as the debug gate with its wipe-on-failure choice, and
the two ten-byte identifiers gate the emulator and the serial programmer
separately. Protections arrive enabled from the factory, and the shield
window, common at this capacity, travels with the capture. The passive
first read of block zero turns all of it into facts.

Access and the bench

0.5 mm leads take a fixture directly and a lift costs minutes; the part
goes back on the board afterwards. The IC decapsulation service route, the firmware extraction service
page and microcontroller unlock cover the escalations in that order.

Row context

The 48-pin siblings are in R5F100GA memory readout through R5F100GH flash data and
R5F100GK code flash extraction and R5F100GL firmware decryption. The 256 KB die in the 44-pin package is
R5F100FJ flash memory. For the boot-swap mechanics, see R5F100FE boot cluster recovery, and
for segmented-image discipline the 128 KB member is under R5F100GG memory dump.

The interrupt budget at forty-eight pins

Seven external interrupt lines, forty-four I/O and ten converter inputs
are the raw material of the motor-drive and relay-bank boards this
member serves, and the vector table shows how the firmware spent them.
Zero-cross detection, fault feedback and communication each claim their
own entry, with the transfer engines carrying the data movement behind
them. Reading that allocation from a capture is fast and locates the
safety-critical code, which is where verification effort concentrates
first.

The capacity itself is the other half of the story. Four 64 KB windows
of banked code, 20 KB of volatile memory and the doubled data store
mark the image as built for field maintenance, with both boot copies
populated and the reservation in the linker map confirming it. A
capture follows the family’s standard walk and a rebuild keeps the four
windows distinct; the 0.5 mm leaded body keeps the physical work
routine from the first probe to the last verification.

Identification from circuit context is quick here: the wide leaded
footprint, the regulator capacitor and the ten-channel sensing plan
separate this member from its 44-pin sibling before any marking is
read.