NXP Semiconductors
QN902x
User Manual of QN902x
UM10996
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© NXP Semiconductors N.V. 2018. All rights reserved.
User Manual
Rev 1.3
— 05 November 2018
53 of 128
PLL, directly from the 16/32 MHz external oscillator, or from 32 kHz (32.768 kHz)
oscillator
The AHB clock is derived from the system clock and serves as a clock source for CPU
HCLK, FCLK, SPI_AHB, GPIO, BLE_AHB and DMA.
The CPU HCLK and FCLK are the clock sources of the core. The SPI_AHB clocks the
internal flash. The BLE_AHB is used for the BLE block and does not need to be
configured. All clocks, except the CPU HCLK and FCLK, can be disabled when
corresponding block is not active.
6.5.2
Configure APB clock
The APB clock is derived from the AHB clock and serves as the clock source for all
registers. Due to the divider, the APB clock is lower than or equal to the core clock.
Because all peripheral registers are clocked by the APB clock, the APB clock should not
be configured slower than the peripheral clocks.
6.5.3
Configure BLE clock
The BLE_AHB is clocked by the AHB clock, and the BLE clock is derived from the AHB
clock. They are used for BLE RF block and usually do not need to be configured by the
user. The BLE clock can only run at 8 or 16 MHz
Note: BLE RF block requires correct configuration of the BLE_AHB and BLE clocks.
Therefore, it is recommended to use the Software Development Kit.
6.5.4
Configure peripheral clocks
The peripheral clocks are derived from the AHB clock. The dividers of all peripheral
blocks clock can be configured independently, therefore, all peripheral clocks can run at
different frequencies.
Every peripheral block can be disabled to reduce the power by disabling/enabling the
corresponding clock independently.
6.6
Register description
The System Registers are based on 0x40000000.
6.6.1
System Clock Register Description
Table 34 System Clock Register
Offset
Name
Description
000h
CRSS
Enable clock gating and set block reset
004h
CRSC
Disable clock gating and clear block reset
008h
CMDCR
Set clock switch and clock divider
00Ch
STCR
Set systick timer STCALIB and STCLKEN
6.6.1.1
CRSS
CRSS is Enable clock gating and set block reset register, address is 0x40000000