The R5F100BA is the 32-pin entry of the RL78/G13 family: 16 KB of code flash,
2 KB of RAM, 4 KB of data flash, eight converter channels and twenty-eight
I/O in a 5 by 5 mm HWQFN with a 0.5 mm pitch. It is the smallest package in
the family that offers a thermal-improved QFN body rather than leads, and it
sits at the capacity where 8-bit architectures were already straining, which
is why replacement designs land here so often. The protection architecture is
family-standard; the package determines the practical route to everything.

QFN geometry and the centre pad

The 32 pins sit on four sides at 0.5 mm pitch and the die pad underneath is
bonded to the board flood. In-circuit access works on the wings where the
layout exposes them, or through vias, and the lifted-part route onto an
adapter is routine when neither exists. The centre pad complicates hot-air
removal slightly, since the flood underneath sinks heat, and the standard
practice of pre-heating the board from below applies. None of this changes
the chip’s behaviour; it changes the time the first byte costs.

Sixteen blocks and the small-image patterns

Sixteen kilobytes divides into sixteen blocks with the boot cluster in the
first four and the swap mirror at 02000H. At this capacity most images skip
the swap feature and the second cluster is empty, which the mirrored option
bytes at 010C0H reveal immediately: present when the feature is enabled,
erased when not. Block 0 still carries the vectors, the four option bytes,
both ten-byte identifiers and the boot flag, and the shipped block
protections are enabled regardless of whether the author configured anything.

The debug gate and the destructive bit

The fourth option byte, 000C3H, decides whether the single-wire debug
interface presents itself and whether a failed ten-byte ID check erases the
array. On replacement-design boards this byte is frequently left at its
permissive default while the serial identifier at 000CEH is populated,
because the production programmer needs the serial path and nobody ever
planned to debug the product. That asymmetry is the most common opening on
this member, and it is discovered by reading block 0 passively before any
active connection is made.

Two KB of RAM and the readout plan

With 2 KB of volatile memory the flash library cannot run from RAM, so
in-circuit rewrite options are limited to the ROM-resident mode and its
restrictions. Readout does not need the library, but the budget still shapes
the job: an in-circuit streaming loader has to be small, and on boards where
the application is running, the cleanest capture is out of circuit. The part
lifts onto an adapter, the full sixteen blocks and the 4 KB data flash stream
out in one pass, and the option bytes are recorded as found.

The data flash on replacement boards

Designs ported from 8-bit predecessors keep their calibration in the data
flash and often leave the wear-levelled structure inherited from the older
EEPROM-emulation code. The array’s content is what makes a replacement board
regulate like the original, and its history explains the unit’s service life.
Recovering both arrays with their option-byte context is the standard
deliverable, and the reproduction path that uses them is described on the
IC clone service page.

Row context

The 32-pin members with more memory are in R5F100BC flash heximal through
R5F100BG flash data, the 30-pin leaded equivalents start at R5F100AA flash data, and
the 36-pin wafer-level row begins at R5F100CA flash memory. For the same capacity in
a leaded 20-pin package, see R5F1006A flash memory. Architecture comparisons with
the direct 8-bit predecessors, whose protection was a single fuse bit, are in
MC68HC08AZ60 eeprom memory recovery, and the general entry point for the family is the
MCU crack service page.

Twenty-eight lines in a five millimetre square

The 32-pin QFN fits twenty-eight I/O, six external interrupts and eight
converter inputs around a 5 by 5 mm body, an I/O density the older 8-bit
parts this family replaces never approached. Six of the lines are
open-drain with a six-volt withstand, enough to sit directly against
mains-referenced circuitry through the usual dividers. For bench planning
the density cuts both ways: more of the board’s signals terminate at the
part, so a fixture that reaches the package reaches nearly everything, but
the same pitch that helps the probe also means any lifted lead is a
microscope job.