SN8P26L38
8-Bit Micro-Controller
SONiX TECHNOLOGY CO., LTD
Page 50
Version 1.5
4
SYSTEM CLOCK
4.1
OVERVIEW
The micro-controller is a dual clock system. There are high-speed clock and low-speed clock. The high-speed clock is
generated from the external oscillator circuit or on-chip 8MHz high-speed RC oscillator circuit (IHRC 8MHz). The
low-speed clock is generated from on-chip low-speed RC oscillator circuit (ILRC 10KHz @3V).
Both the high-speed clock and the low-speed clock can be system clock (Fosc). The system clock in slow mode is
divided by 4 to be the instruction cycle (Fcpu).
Normal Mode (High Clock):
Fcpu = Fhosc / N
, N = 1 ~ 8, Select N by Fcpu code option.
Slow Mode (Low Clock):
Fcpu = Flosc/4.
4.2
CLOCK BLOCK DIAGRAM
Fhosc.
Fcpu = Fhosc/1 ~ Fhosc/8
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 10KHz@3V).
Fosc: System clock source.
Fcpu: Instruction cycle.
4.3
Fcpu (INSTRUCTION CYCLE)
Fcpu is instruction cycle which is divided from the system high clock source and decides the system operating rate.
Fcpu rate is selected by code option from Fhosc/1~Fhosc/8 If the system high clock source is from external 16MHz
crystal, and the Fcpu code option is Fhosc/4, the Fcpu frequency is 16MHz/4 = 4MHz. The code option doesn
’t support
slow mode because the Fcpu of slow mode is fixed Flosc/4 condition.
In high noisy environment, below
“Fhosc/4” of Fcpu code option is the strongly recommendation to reduce
high frequency noise effect.
