SN8P2501D
8-Bit Micro-Controller
SONiX TECHNOLOGY CO., LTD
Page 39
Version 1.5
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/1 ~ Fhosc/16, Noise Filter Disable.
Fcpu = Fhosc/4 ~ Fhosc/16, Noise Filter Enable.
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, 32KHz@5V).
Fosc: System clock source.
Fcpu: Instruction cycle.
SONIX provides a
“Noise Filter”
controlled by code option. In high noisy situation, the noise filter can isolate noise
outside and protect system works well. The minimum Fcpu of high clock is limited at
Fhosc/4
when noise filter enable.
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/1~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.
In high noisy environment, below
“Fhosc/4” of Fcpu code option is the strongly recommendation to reduce
high frequency noise effect.
