ML51/ML54/ML56
Sep. 01, 2020
Page
292
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Rev 2.00
ML
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54
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ML51/M
L54
/M
L56
Series
Tec
hnical Reference
Manual
6.2 System Manager
6.2.1
Clock System
The ML51/ML54/ML56 Series has a wide variety of clock sources and selection features that allow it
to be used in a wide range of applications while maximizing performance and minimizing power
consumption. The ML51/ML54/ML56 Series provides five options of the system clock sources
including internal oscillator, crystal/resonator, or external clock from X
IN
pin via software. The
ML51/ML54/ML56 Series is embedded with two internal oscillators: one 38.4 R/W low-speed and one
24 R/W high-speed, which is factory trimmed to ±2% under all conditions. A clock divider CKDIV is
also available on ML51/ML54/ML56 Series for adjustment of the flexibility between power
consumption and operating performance.
32.768 kHz
Oscillating
Circuit
24 MHz Internal
Oscillator
XOUT
XIN
OSC[2:0]
(CKSWT[2:0])
F
OSC
CPU
Peripherals
38.4 kHz
Internal
Oscillator
Flash
Memory
F
HIRC
F
LIRC
Clock
Divider
F
SYS
Watchdog
Timer
CKDIV
Clock
Filter
CLO
CLOEN
(CKCON.1)
F
LXT
4~24 MHz
Oscillating
Circuit
F
HXT
F
ECLK
10X
01X
00X
Self
Wake-up
Timer
0
1
WKTCK
(WKCON.5)
[1]
Default system clock source after power-on
[1]
X32OUT
X32IN
110
111
Figure 6.2-1 Clock System Block Diagram
System Clock Sources
6.2.1.1
There are a total of three system clock sources selectable in the ML51/ML54/ML56 Series including
high-speed internal oscillator, low-speed internal oscillator and external clock input. Each of them can
be the system clock source in the ML51/ML54/ML56 Series. Different active system clock sources
also affect multi-function of P5.3/X
IN
,
P5.2/X
OUT
and
P5.5/X
32
I
N
,
P5.4/X32
OUT
pins.
Internal Oscillators
6.2.1.2
There are two internal oscillators in the ML51/ML54/ML56 Series
– one 24 R/W high-speed internal
oscillator (HIRC) and one 38.4 R/W low-speed (LIRC). Both of them can be selected as the system
clock. HIRC can be enabled by setting HIRCEN (CKEN.5). LIRC is enabled after device is powered
up. User can set OSC[2:0] (CKSWT [2:0]) as [0,0,x] to select the HIRC as the system clock. By setting
