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UM10503
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© NXP B.V. 2015. All rights reserved.
User manual
Rev. 2.1 — 10 December 2015
166 of 1441
NXP Semiconductors
UM10503
Chapter 13: LPC43xx/LPC43Sxx Clock Generation Unit (CGU)
13.2.1.1 Changing the BASE_M4_CLK after power-up, reset, or deep power-down
mode
The following procedure shows how to change the default setting of the core clock
(BASE_M4_CLK = 96 MHz; IRC = PLL1 clock source) to an operating frequency above
110 MHz while also changing the clock source from IRC to crystal oscillator:
1. Select the IRC as BASE_M4_CLK source.
2. Enable the crystal oscillator (see
3. Wait 250
s.
4. Reconfigure PLL1 as follows (see
):
–
Select the M and N divider values to produce the final desired PLL1 output
frequency f
outPLL
.
–
Select the crystal oscillator as clock source for PLL1.
5. Wait for the PLL1 to lock.
6. Set the PLL1 P-divider to divide by 2 (DIRECT = 0, PSEL=0).
7. Select PLL1 as BASE_M4_CLK source. The BASE_M4_CLK now operates in the
mid-frequency range.
8. Wait 50
s.
9. Set the PLL1 P-divider to direct output mode (DIRECT = 1).
The BASE_M4_CLK now operates in the high-frequency range.
13.2.1.2 Changing the BASE_M4_CLK after waking up from deep-sleep or
power-down modes
The following procedure shows how to ramp up the BASE_M4_CLK clock from low
frequencies to the high frequency range (see
). This procedure applies after
waking up from deep-sleep or power-down modes and any time the part runs at
frequencies < 90 MHz.
1. If the crystal oscillator is powered down, enable the crystal oscillator (see
and wait 250
s.
2. Select the crystal oscillator as clock source for BASE_M4_CLK (see
).
3. Reconfigure PLL1 as follows (see
):
–
Select the M and N divider values to produce the final desired PLL1 output
frequency f
outPLL
.
–
Select the crystal oscillator as clock source for PLL1.
4. Wait for the PLL1 to lock.
5. Set the PLL1 P-divider to divide by 2 (DIRECT = 0, PSEL=0).
6. Select PLL1 as BASE_M4_CLK source. The BASE_M4_CLK now operates in the
mid-frequency range.
7. Wait 50
s.
8. Set the PLL1 P-divider to direct output mode (DIRECT = 1).
The BASE_M4_CLK now operates in the high frequency range (110 MHz to 204 MHz).