MS51
Nov. 28, 2019
Page
204
of 491
Rev 1.00
MS51
32K
SE
RIES
TE
CHNICAL RE
F
EREN
CE MA
N
UAL
RCTRIM1
–High Speed Internal Oscillator 16 MHz Trim 1
Register
SFR Address
Reset Value
RCTRIM1
85H, All pages, TA protected
0000_0000b
7
6
5
4
3
2
1
0
-
-
-
HIRC24
-
-
-
HIRCTRIM.0
-
-
-
R/W
-
-
-
R/W
Note:
since defaut RCTRIM0 and RCTRIM1 value is base on 16 MHz, if base on this value then
modify HIRC24(RCTIM1.4) to enable 24 MHz HIRC mode, the real HIRC deviation will more than 1%.
Suggest reload the 24 MHz HIRC value from after UID, and check value bit 4 to confirm this value is
suit for 24 MHz application.
External Crystal/Resonator or Clock Input
6.2.1.4
There are three possible clock source options of external clock sources
– 4 MHz to 24 MHz high-
speed crystal/resonator (HXT), and the external clock input (ECLK) through X
IN
pin. User can set
OSC[2:0] as [0,1,x] to select ECLK as the system clock. By setting OSC[2:0] as [1,1,0], HXT will be
selected as the system clock. When HXT is used as the system clock, X
IN
and X
OUT
are the input and
output, respectively, of an internal inverting amplifier. A crystal or resonator should be connected
between X
IN
and X
OUT
pins. When enabling and selecting ECLK as the system clock source, the
system clock is supplied via the X
IN
pin. The common application is to drive X
IN
with an active
oscillator or clocks from another host device. Be aware that user should never feed any clock signal
larger than voltage 2.4V to X
IN
and give a DC voltage to X
OUT
pin which value is half of X
IN
, when
ECLK mode is selected. Otherwise, it may break the device.
