LPC5411x PLL settings

yhc123 — Sun, 15 Feb 2026 05:28:35 GMT

In my current project, I am using the PLL module of the LPC5411x. According to Section 6.5.49.6 of the datasheet, the N, M, and P values of the PLL must be calculated before being written into the corresponding registers.

However, in SDK_2_9_0_LPCXpresso54114, the calculation code for NDEC, MDEC, and PDEC is not implemented; instead, the SDK directly writes manually pre‑calculated values into the syspllndec register, as shown below. (I want set M=75, so I need to calculate MDEC=9637 manually and set it to SYSCON_SYSPLLSSCTRL0_MDEC)

May I ask whether there are plans to add the calculation functions in SDK for NDEC, MDEC, and PDEC in future SDK releases?
Currently, setting NDEC, MDEC, and PDEC is not intuitive and is difficult to maintain, as every change to M, N, or P requires recalculating the corresponding NDEC, MDEC, and PDEC values manually.

Thanks

Re: LPC5411x PLL settings

carlos_o — Mon, 16 Feb 2026 22:56:36 GMT

Hi @yhc123

Thanks for your post.

Currently, there are no plans to release a new SDK version for the LPC5411. Any required calculation would need to be implemented on your side. We apologize for the inconvenience this may cause.

topic LPC5411x PLL settings in LPC Microcontrollers

LPC5411x PLL settings

Re: LPC5411x PLL settings