LPC54618 System PLL Registers

evan_ohlsen — Mon, 18 Oct 2021 18:45:32 GMT

I am having a great deal of trouble setting the multiply / divide registers for the System PLL clock, specifically the MDEC register, SYSPLLCTRL, SYSPLLMDEC, SYSPLLNDEC, and SYSPLLPDEC.

The function "BOARD_BootClockPLL180M" in the SDK sets the boot clock to 180MHz, and uses the interal 12MHz FRO as the input to the system PLL, and sets MDEC, NDEC, and PDEC, using hard-coded values: 8191, 770, and 98 respectively.

There is pseudo-code provided in the reference manual for calculating the MDEC register value, but when I try to calculate it, I get a different number than what is in the example in the SDK.

Looking for help because I would like to generate a 144MHz boot clock from the System PLL, but I cannot decipher this section of the reference manual. Would prefer NOT installing MCUXpresso or any software tools. Just looking for how these register values are actually calculated.

Thank you for your help,

Evan

--UPDATE--

I realize this is over a year later, but I just remembered this and wanted to leave it out there for anyone who may need it in the future! Messing around a bit, I found a way to encode the MDEC register value for any given multiplier M and made a handy function for doing so. Cheers!

uint32_t EncodeMDEC(uint16_t M)
{
uint32_t x, MDEC = 0;

/* Find MDec */
switch (M)
{
case 0:
MDEC = 0x1FFFF;
break;
case 1:
MDEC = 0x18003;
break;
case 2:
MDEC = 0x10003;
break;
default:
x = 0x04000UL;
//uint32_t m = 0xFFFFFFFFUL;
for (uint32_t i = 0x8000; i >= 3UL; i--)
{
x = (((x ^ (x >> 1UL)) & 1UL) << 14UL) | ((x >> 1UL) & 0x3FFFUL);
if(i == M)
{
MDEC = (x & 0x1FFFF);
}
}
break;
}
return MDEC;
}

Re: LPC54618 System PLL Registers

gusarambula — Tue, 06 Oct 2020 19:39:29 GMT

Hello Evan,

I understand that you may prefer not to install additional tools or IDEs, but it is the easiest way to setup the PLLs for your application, albeit not the only one.

If you are open to a compromise you may install the MXUXpresso Config Tools as stand alone so that you can use the Clocks Config Tool, which makes the process much less cumbersome.

Alternatively, if you rather not install any additional software at all, you may use the web version of the Clock Config Tool to aid on the setup of the PLL registers.

Go to the MXUCpresso Builder homepage (link below) and after selecting your board you may build the MCUXpresso SDK or explore the Pins Tool and Clocks Tool on the web.

https://mcuxpresso.nxp.com/en/select

I hope that this information helps!

Regards,
Gustavo

topic Re: LPC54618 System PLL Registers in LPC Microcontrollers

LPC54618 System PLL Registers

Re: LPC54618 System PLL Registers