MCX MicrocontrollersのトピックRe: MCXW23x — BLE connection drops repeatedly when using FRO32K

MCXW23x — BLE connection drops repeatedly when using FRO32K

LongLeWT — Thu, 17 Sep 2026 14:28:31 GMT

MCXW235B BLE connection drops repeatedly, `disconnect reason=0x08` (LL supervision timeout), consistently a few seconds after connect

Hardware constraint (fixed, not changeable on this design):** the custom board does **not** populate a 32.768kHz crystal on `XI32K`/`XO32K` — both pins are left open. The board only has a 32MHz crystal on `XI32M`/`XO32M`

Re: MCXW23x — BLE connection drops repeatedly when using FRO32K

sofiaurueta — Fri, 18 Sep 2026 23:43:20 GMT

Hello, hope you are doing well.

How are you selecting the clock source in your application?

FRO32K is supported as an option for the BLE sleep clock, as part of the two low-frequency sources available for MCXW23xB: external crystal oscillator XO_32K, and 32.768 kHz freely running oscillator FRO_32K.

The command "HCI_CMD_OCF_LE_SELECT_SLEEP_CLOCK_SOURCE" is used to select the sleep clock source that is used for the sleep timer, where FRO32K is a sleep clock source (slp_clk_src=0x01). In a case where the 32.768 kHz crystal (XO_32K) is absent, the free running oscillator (FRO_32K) can also act as a backup of the 32.768 kHz clocking.

In MCXW23, the frequency of an on-chip or off-chip clock signal can be measured accurately with a selectable reference clock. For example, the frequency measurement function can be used to determine the frequency of the 32.768 kHz free running oscillator (FRO32K) accurately, using the frequency measure function control register (FREQ_ME_CTRL). To start a frequency measurement cycle and read the result, see MCXW23 Reference Manual Section 11.4.1. The FRO32K trim registers are available in RM section 45.4.11.2.13 FRO32K control (FRO32K)

Best regards,
Sofia.

Re: MCXW23x — BLE connection drops repeatedly when using FRO32K

LongLeWT — Mon, 21 Sep 2026 03:44:28 GMT

Dear sofiaurueta,

Thanks for your reply.

We also tested ll_intf_curb_sleep_state(1) to disable sleep, which returned 0. After reviewing the code, we couldn't find any explicit sleep commands. Furthermore, ll_intf_le_select_slp_clk_src(RTC_SLPTMR) was configured with value 0x02, corresponding to the RTC clock source.

Additionally, we integrated FSCI into the Wireless UART sample and tested Peripheral mode, where we observed the following RX data when connecting via phone.

Best Regards,