SN8F2255B datasheet(46/133 Pages) SONIX

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SN8F2250B Series

USB 2.0 Full-Speed 8-Bit Micro-Controller

SONiX TECHNOLOGY CO., LTD

Page 46

Version 1.1

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 & on-chip PLL circuit. The low-speed clock is generated from on-chip low-speed

RC oscillator circuit (ILRC 24 KHz).

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 ~ 4, Select N by Fcpu code option.

Slow Mode (Low Clock):

Fcpu = Flosc/4.

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 CLOCK BLOCK DIAGRAM

Fhosc.

Fcpu = Fhosc/1 ~ Fhosc/4, Noise Filter Disable.

Fcpu = Fhosc/4, Noise Filter Enable.

Flosc.

Fcpu = Flosc/4

CPUM[1:0]

XIN

XOUT

STPHX

HOSC

Fcpu Code Option

Fosc

CLKMD

Fcpu

HOSC: High_Clk code option.

Fhosc: External high-speed clock.

Flosc: Internal low-speed RC clock (Typical 24 KHz).

Fosc: System clock source.

Fcpu: Instruction cycle.

SN8F2255B Datasheet(PDF) 46 Page - SONiX Technology Company