lpcware

LPC1768 maximum frequency is really 100MHz?

Discussion created by lpcware Employee on Jun 15, 2016
Latest reply on Jun 15, 2016 by lpcware
Content originally posted in LPCWare by giusloq on Tue Jan 12 06:13:33 MST 2016
I started with a new board based on LPC1768. I started with some files available from NXP examples and I call the funcion Chip_SetupIrcClocking().

void Chip_SetupIrcClocking(void)
{
/* Disconnect the Main PLL if it is connected already */
if (Chip_Clock_IsMainPLLConnected()) {
Chip_Clock_DisablePLL(SYSCTL_MAIN_PLL, SYSCTL_PLL_CONNECT);
}

/* Disable the PLL if it is enabled */
if (Chip_Clock_IsMainPLLEnabled()) {
Chip_Clock_DisablePLL(SYSCTL_MAIN_PLL, SYSCTL_PLL_ENABLE);
}

Chip_Clock_SetCPUClockDiv(0);
Chip_Clock_SetMainPLLSource(SYSCTL_PLLCLKSRC_IRC);

/* FCCO = ((44+1) * 2 * 4MHz) / (0+1) = 360MHz */
Chip_Clock_SetupPLL(SYSCTL_MAIN_PLL, 44, 0);

Chip_Clock_EnablePLL(SYSCTL_MAIN_PLL, SYSCTL_PLL_ENABLE);

Chip_Clock_SetCPUClockDiv(2);
while (!Chip_Clock_IsMainPLLLocked()) {} /* Wait for the PLL to Lock */

Chip_Clock_EnablePLL(SYSCTL_MAIN_PLL, SYSCTL_PLL_CONNECT);
}


It seems to me that function configures the CPU with a 120MHz. I measured 12MHz frequency at CLKOUT pin (configured with a divisor of 10). The chip seems working well.

Am I overclocking the CPU and its running is not reliable in this condition?

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