SN8P2740 Series
ADC, OP-amp, Comparator 8-Bit Micro-Controller
SONiX TECHNOLOGY CO., LTD
Page 44
Version 2.0
4
4
4
SYSTEM CLOCK
4.1 OVERVIEW
The micro-controller is a dual clock system including high-speed and low-speed clocks. The high-speed clock includes
internal high-speed oscillator and external oscillators selected by
“High_CLK” code option. The low-speed clock is from
internal low-speed oscillator controlled by
“CLKMD” bit of OSCM register. Both high-speed clock and low-speed clock
can be system clock source through a divider to decide the system clock rate.
High-speed oscillator
Internal high-speed oscillator is 16MHz RC type called
“
IHRC
”.
External high-speed oscillator includes crystal/ceramic (4MHz, 12MHz, 32KHz) and RC type.
Low-speed oscillator
Internal low-speed oscillator is 16KHz @3V, 32KHz @5V RC type called
“
ILRC
”.
System clock block diagram
Fhosc.
Fcpu = Fhosc/4 ~ Fhosc/16
Flosc.
Fcpu = Flosc/4
CPUM[1:0]
XIN
XOUT
STPHX
HOSC
Fcpu Code Option
Fosc
Fosc
CLKMD
Fcpu
HOSC: High_Clk code option.
Fhosc: External high-speed clock / Internal high-speed RC clock.
Flosc: Internal low-speed RC clock (about 16KHz@3V and @5V).
Fosc: System clock source.
Fcpu: Instruction cycle.
4.2 FCPU (INSTRUCTION CYCLE)
The system clock rate is instruction cycle called
“
Fcpu
” which is divided from the system clock source and decides the
system operating rate. Fcpu rate is selected by Fcpu code option and the range is
Fhosc/4~Fhosc/16
under system
normal mode. If the system high clock source is external 4MHz crystal, and the Fcpu code option is Fhosc/4, the Fcpu
frequency is 4MHz/4 = 1MHz. Under system slow mode, the Fcpu is fixed Flosc/4, 16KHz/4=4KHz @3V,
32KHz/4=8KHz @5V.
4.3 SYSTEM HIGH-SPEED CLOCK
The system high-speed clock has internal and external two-type. The external high-speed clock includes 4MHz, 12MHz,
32KHz crystal/ceramic and RC type. These high-speed oscillators are selected by
“
High_CLK
” code option.