NXP Semiconductors
UM10858
PN7462 family HW user manual
UM10858
All information provided in this document is subject to legal disclaimers.
© NXP B.V. 2018. All rights reserved.
User manual
COMPANY PUBLIC
Rev. 1.4 — 14 May 2018
314514
57 of 345
•
Wait for system reset release
•
Wait for 4 clk_lfo clock cycles (4x(1/380 KHz) ~ 10.53 us)
•
Set XTAL_ENABLE_KICK to ’1’
•
Wait for 4 clk_lfo clock cycles (4x(1/380 KHz) ~ 10.53 us)
•
Set XTAL_ENABLE_KICK to ’1’
In case of error, the PCR can try to restart the XTAL activation sequence by activating the
system reset again or switching to another system clock source.
The XTAL can also be controlled by software when
CLKGEN_HFO_XTAL_REG.XTAL_CONTROL_SW is set to ’1’. Before activating the
XTAL software control, the system clock should be switched from the XTAL to another
clock. The following sequence must be followed step by step in order to activate XTAL
by SW.
1.
Set CLKGEN_HFO_XTAL_REG.XTAL_CONTROL_SW is set to ’1’.
2.
Clear CLK_HFO_XTAL_REG.XTAL_SPARE0 to ‘0’
3.
Wait for 4 clk_lfo clock cycles (4x(1/380 KHz) ~ 10.53 us)
4.
Clear CLKGEN_HFO_XTAL_REG.XTALl_BYPASS to ‘0’
5.
Clear CLKGEN_HFO_XTAL_REG.XTAL_SELECT_EXTERNAL_CLOCK to ‘0’
6.
Set XTAL_ENABLE_KICK to ’1’
7.
Wait for 4 clk_lfo clock cycles (4x(1/380 KHz) ~ 10.53 us)
8.
Set XTAL_ENABLE_KICK to ’1’
7.1.2 High Frequency Oscillator (HFO)
The PN7462 family integrates an internal low power High Frequency Oscillator (HFO),
generating a 20 MHz clock without using the PLL. The HFO can be used as a system
clock. The HFO is activated by default with the
CLKGEN_HFO_XTAL_REG.HFO_ENABLE register bit as soon as the system reset is
released.
7.1.3 Low Frequency Oscillator (LFO)
The PN7462 family integrates an internal low power Low Frequency Oscillator working at
380 kHz. The LFO is used by the EEPROM, POR sequencer, Contactless interface,
timers and watchdog. The LFO needs to be activated to start the XTAL Oscillator
7.2 Phase Locked Loop (USB PLL)
The PN7462 family integrates a dedicated USB PLL to generate a low-noise 48 MHz
clock signal from the 27.12 MHz input signal coming from the external crystal (XTAL).
The 48 MHz clock signal is used as the main clock for the USB interface.
