When a 256 KB controller is qualified to 125°C, the design is usually doing something that cannot be allowed to stop: a pump that must keep running, a compressor that must not seize, a heating stage that must not overshoot. Losing the firmware on such a unit is not an inconvenience, it is a production stop. R5F35L2EKFE is the part at that intersection – largest array, 80 pins, K-grade.
What A Dead Unit Still Tells You
Even with no power applied, three things are recoverable before the array is touched: the package marking, the crystal frequency, and the external memory or peripheral wiring visible on the board. Those three narrow the model to a handful of candidates, and the memory size confirms it. If the marking is a house code, the array size and the pin count identify the device within the group.
Memory And Temperature Together
| Property | Value |
|---|---|
| Program ROM 1 | 256 KB, C0000h to FFFFFh |
| Program ROM 2 | 16 KB, 10000h to 13FFFh |
| Data flash | 8 KB, two 4 KB blocks |
| RAM | 20 KB, 00400h to 053FFh |
| Temperature | -40 to 125°C |
| Package | 80-pin LQFP |
The temperature rating has a practical consequence for the read: K-grade boards are often mounted on aluminium or potted to survive vibration, and both make pad access harder. A photograph of the assembly decides whether the read happens in place or after removal, and it is worth taking before the unit is shipped.
The Option Window
OFS1 and OFS2 sit in the last 37 bytes of the map, together with the ID code. On high-temperature designs these often carry a deliberately conservative low-voltage detect setting, because a brown-out at 100°C behaves differently from one at room temperature. A merged image that omits the window may boot on the bench and reset unpredictably in the application. We include the window and report the values in plain text.
Sequence And Checks
Data flash block A, block B, ROM 2, ROM 1 from C0000h, then the option window. Every pass is duplicated; a mismatch gets a third pass and, if it persists, a different acquisition path for that region. The checksums shipped with the files are the checksums of the delivered regions, not of an intermediate buffer.
What Is Not Recoverable
Symbol names, comments, and the original build configuration are gone. The hex is what a compiler emitted. If the customer needs to modify the firmware, the practical route is to re-implement around the recovered image by matching observed behaviour, which is a different and usually larger job than a copy.
What A 125°C Rebuild Has To Reproduce
Temperature qualification is not only about the part. A replacement built from a recovered image also has to reproduce the option bytes that set low-voltage detection, the watchdog window, and the reset pin behaviour, because those interact with the supply ramp at temperature extremes.
Two of the three are in flash and come with the dump. The third – the watchdog window – is usually configured in software at start-up, which means it is visible in the image but only if the rebuild team knows to look for the register write. A note in the report pointing at that sequence saves a debugging cycle.
Documenting The Thermal Path
Boards rated to 125°C are mounted for heat, not for service. That has a practical consequence for a read: the thermal interface material, the clamp pressure and the presence of a heatsink are all part of the assembly, and disturbing them can change the behaviour of a unit that is returned to service.
Where the read can be done in place, the assembly is left alone. Where it cannot, the parts that were removed are documented and returned with the unit, so the customer can re-assemble to the original specification rather than guessing at the torque and the compound.
Getting Started
Send the unit, the supply rail, and the failure description. If the product has a field-update path, say so, because the boot code in ROM 2 then has to be preserved exactly. The services page covers packing; the contact form is quicker for a technical question. Related: R5F35L2EJFE for the commercial grade, R5F35L3EKFF for the 64-pin equivalent.