MS51
Dec. 17, 2019
Page
155
of 316
Rev 1.01
M
S51
SE
RIES
TE
CHNICA
L REF
ERE
N
CE MA
NU
A
L
CKSWT
– Clock Switch (TA protected)
Regiser
Address
Reset Value
CKSWT
96H, all pages, TA protected
0011_0000b
7
6
5
4
3
2
1
0
-
-
HIRCST
-
ECLKST
OSC[1:0]
-
-
-
R
-
R
W
-
Bit
Name
Description
7:6
-
Reserved
5
HIRCST
High-speed internal oscillator 16 MHz status
0 = High-speed internal oscillator is not stable or disabled.
1 = High-speed internal oscillator is enabled and stable.
4
-
Reserved
3
ECLKST
External clock input status
0 = External clock input is not stable or disabled.
1 = External clock input is enabled and stable.
2:1
OSC[1:0]
Oscillator selection bits
This field selects the system clock source.
00 = Internal 16 MHz oscillator.
01 = External clock source according to EXTEN[1:0] (CKEN[7:6]) setting.
10 = Internal 10 kHz oscillator.
11 = Reserved.
Note that this field is write only. The read back value of this field may not correspond to the
present system clock source.