Every few months a board arrives with a BOM that names a part Artery does not make. AT32F425RCT7 is one of those names. The family exists, the 64-pin package exists, and the temperature code exists, but the flash letter does not: the AT32F425 line is offered in 32 KB and 64 KB only, so there is no 256 KB member for a C to describe.
The Code Letter That Does Not Exist
Artery’s numbering uses position four for density: 4 is 16 KB, 6 is 32 KB, 8 is 64 KB, B is 128 KB, C is 256 KB, G is 1 MB. The F425 tops out at 8. Its published table lists F8P7, K8T7, K8U7-4, C8U7, C8T7, R8T7-7 and R8T7 for 64 KB, and the same suffixes beginning with 6 for 32 KB. Nothing carries a C.
The likely origin of the mistake is a cross-reference table: the F425 is positioned against entry-level Cortex-M0 and M0+ parts, and a substitution sheet that maps an STM32F072 or an STM32F030 to “the Artery equivalent” can pick up a density that the equivalent does not have. The second likely origin is a copy-paste from the F423 row, which does have a 256 KB member and does use C.
What The 64-Pin Part Actually Is
Take the suffix as R8T7: 64 pins in a 10 by 10 millimetre LQFP (R8T7-7 is the 7 by 7 outline, same die). Inside: a 96 MHz Cortex-M4 with DSP instructions and no FPU, 64 KB of flash, 4 KB of system memory that can be converted once into user code, 20 KB of SRAM with parity checking, 55 GPIO, sixteen ADC channels, one CAN controller with 256 bytes of dedicated buffer, a full-speed USB device controller with 1280 bytes of buffer that runs without a crystal, and twenty-four channels of PWM from a timer set that includes one advanced block.
Twenty KB of SRAM on a 96 MHz part is the constraint that shapes firmware here. Buffers are small, stacks are small, and code tends to be written tightly with lookup tables placed in flash.
Protection On A Small Part
Three mechanisms apply, and they are independent.
The first is access protection over the whole array, which blocks debug and in-system programming and is removed only by an operation that erases everything. The second is per-sector erase and program protection through the EPP bytes, set in 1 KB steps on this family because the device is below 256 KB. The third is sLib, a password-protected range that executes but returns 0xFF to any data read.
Because the array is only 64 KB, the library granularity is 1 KB, and the four-kilobyte floor still applies: the vector table and startup code cannot be inside the library, so the opening four kilobytes of every F425 remain readable unless the whole-array protection is also set.
Permanent Means Permanent
There is a fourth state that is not really a protection level but a one-way door: the advanced access protection mode offered on this series disables the debug interface and cannot be undone by any tool, including the vendor’s own programmer. A part in that state will not answer a debugger, will not accept a loader connection, and looks electrically healthy.
We check for it before quoting a physical route, because it changes the method and the risk. If a customer’s own production line set that byte, no recovery of the debug path is possible and the work moves to the die itself.
If The Wrong Part Is In Hand
Practical advice for the customer who has already populated boards: confirm the marking against the family table, then decide which part the design actually needs. If 64 KB is enough, the read is straightforward and cheap. If the firmware genuinely needs 256 KB, the board carries the wrong chip and no read will fix that — the F423 is the family with a 256 KB member and a similar peripheral set.
What We Ask For
Marking photographs of two units, a schematic extract showing the boot and debug pins, and a statement of whether the board still boots. With those three we can usually confirm the true part number before the parcel is opened, which saves a week and a wasted shipment.
The 48-pin member of the same line is covered in extracting locked AT32F425CCT7 software; the value-line part with the same 64 KB array is at copying a locked AT32F421C8T7 heximal. For the general picture of what each protection layer stops, read reading an IC to bypass protection, and for turnaround see services.