STM32F103C8T6 always shows “SLEEP” in CubeProgrammer, cannot perform full chip erase—no user code loaded

Melih-- · ‎2025-08-16

Hi everyone,
I'm working with an STM32F103C8T6. Even though I haven't programmed any code onto it myself, when I connect with STM32CubeProgrammer, the Registers panel immediately shows “SLEEP” (while on other ST boards it would show “HALTED”). Because of this, I can't perform a Full Chip Erase — the option appears but doesn't work.

Here’s what I’ve tried:

Connected only SWDIO, SWCLK, GND, and 3.3 V (no NRST).
CubeProgrammer shows “SLEEP,” and erase fails.
On other boards, “Connect under reset” works fine and allows erasing.

Possible issues I suspect:

No NRST pin connection → ST-Link can’t halt the MCU before it runs.
Option Bytes might have RDP (Read-Out Protection) enabled.
BOOT0 pin wrongly tied (stuck in System Memory mode).
Some factory test code or previous user code (making MCU go to sleep on reset).

What I tried from forum suggestions:

Tried “Connect under reset” with NRST — this works on other boards but seems not to work here yet.

Any ideas how to force-erase or regain access?
I’d appreciate any advice—including Option Bytes configuration, hardware wiring, or CubeProgrammer settings.
Thanks!