SN8P2740 Series
ADC, OP-amp, Comparator 8-Bit Micro-Controller
4.5 OSCM REGISTER
The OSCM register is an oscillator control register. It controls oscillator status, system mode.
095H
OSCM
Read/Write
After reset
Bit 7
0
-
Bit 6
0
-
Bit 5
0
-
Bit 4
CPUM1
R/W
Bit 3
CPUM0
R/W
Bit 2
CLKMD
R/W
Bit 1
STPHX
R/W
Bit 0
0
-
-
-
-
0
0
0
0
-
Bit 1
STPHX: External high-speed oscillator control bit.
0 = External high-speed oscillator free run.
1 = External high-speed oscillator free run stop. Internal low-speed RC oscillator is still running.
Bit 2
CLKMD: System high/Low clock mode control bit.
0 = Normal (dual) mode. System clock is high clock.
1 = Slow mode. System clock is internal low clock.
Bit[4:3]
CPUM[1:0]: CPU operating mode control bits.
00 = normal.
01 = sleep (power down) mode.
10 = green mode.
11 = reserved.
“STPHX” bit controls internal high speed RC type oscillator and external oscillator operations. When “STPHX=0”, the
external oscillator or internal high speed RC type oscillator active. When “STPHX=1”, the external oscillator or internal
high speed RC type oscillator are disabled. The STPHX function is depend on different high clock options to do
different controls.
IHRC_16M: “STPHX=1” disables internal high speed RC type oscillator.
RC, 4M, 12M, 32K: “STPHX=1” disables external oscillator.
4.6 SYSTEM CLOCK MEASUREMENT
Under design period, the users can measure system clock speed by software instruction cycle (Fcpu). This way is
useful in RC mode.
Example: Fcpu instruction cycle of external oscillator.
B0BSET
P0M.0
; Set P0.0 to be output mode for outputting Fcpu toggle signal.
@@:
B0BSET
B0BCLR
JMP
P0.0
P0.0
@B
; Output Fcpu toggle signal in low-speed clock mode.
; Measure the Fcpu frequency by oscilloscope.
Note: Do not measure the RC frequency directly from XIN; the probe impendence will affect the RC
frequency.
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