UM10850
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© NXP B.V. 2016. All rights reserved.
User manual
Rev. 2.4 — 13 September 2016
28 of 464
NXP Semiconductors
UM10850
Chapter 4: LPC5410x System configuration (SYSCON)
–
The RTC 32 kHz oscillator
Section 4.5.16 “Main clock source select register A”
and
.
2. Select the divider value for the system clock. A divider value of 0 disables the system
clock.
Section 4.5.29 “System clock divider register”
3. Select the memories and peripherals that are operating in the application and
therefore must have an active clock. The core is always clocked.
Section 4.5.22 “AHB Clock Control register 0”
Section 4.5.23 “AHB Clock Control
.
4.2.3 Measure the frequency of a clock signal
The frequency of any on-chip or off-chip clock signal can be measured accurately with a
selectable reference clock. For example, the frequency measurement function can be
used to accurately determine the frequency of the watchdog oscillator which varies over a
wide range depending on process and temperature.
The clock frequency to be measured and the reference clock are selected in the input mux
block. See
Section 8.6.4 “Frequency measure function reference clock select register”
and
Section 8.6.5 “Frequency measure function target clock select register”
Details on the accuracy and measurement process are described in
To start a frequency measurement cycle and read the result, see
4.3 Pin description
4.4 General description
4.4.1 Clock generation
The system control block facilitates the clock generation. Many clocking variations are
possible.
gives an overview of potential clock options. The maximum clock
frequency is 100 MHz.
Remark:
In order for any of the clock multiplexers shown in
to operate, the
currently selected clock must be running, and the clock to be switched to must also be
running. This is so that the multiplexer can gracefully switch between the two clocks
without glitches.
Table 26.
SYSCON pin description
Function
Direction
Pin
Description
Reference
CLKOUT
O
PIO0_21
CLKOUT clock output.
CLKIN
I
PIO0_22
External clock input.