Rainbow-electronics ATmega8515L Manuel d'utilisateur télécharger pdf (Page 93)

ATmega8515(L)

2512A–AVR–04/02

theedge detector usessampling, themaximum frequency of an externalclock it can

detectishalf the sampling frequency (Nyquist sampling theorem). However, due to vari-

ation of the system clock frequency andduty cycle causedbyOscillatorsource (crystal,

resonator, andcapacitors) tolerances, it isrecommended that maximum frequency of an

externalclock sourceisless than f

clk_I/O

/2.5.

An externalclock source can not be prescaled.

Figure 45. Prescalerfor Timer/Counter0and Timer/Counter1

(1)

Note: 1. The synchronization logic on theinput pins(T1/T0) isshowninFigure 44.

Special Function IO Register –

SFIOR

• Bit 0 – PSR10: Prescaler Reset Timer/Counter1 and Timer/Counter0

When thisbit iswrittentoone, theTimer/Counter1and Timer/Counter0 prescalerwill be

reset. The bit will be clearedbyhardwareafter theoperation isperformed. Writing a

zerotothisbit will havenoeffect. Note that Timer/Counter1and Timer/Counter0 share

the same prescaler and a reset of thisprescalerwill affect both timers.Thisbit will

always be read aszero.

PSR10

Clear

clk

I/O

Synchronization

Bit 76543 210

– XMBK XMM2 XMM1 XMM0 PUD –PSR10SFIOR

Read/Write R/W R/W R/W R/W R/W R/W R/W R/W

Initial Value 0 0 0 0 0 0 0 0

1 2 ... 88 89 90 91 92 93 94 95 96 97 98 ... 222 223

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Rainbow-electronics ATmega8515L Manuel d'utilisateur Page 93