Rainbow-electronics ATmega8515L Bedienungsanleitung PDF herunterladen (Seite 119)

119

ATmega8515(L)

2512A–AVR–04/02

When the ICR1 is used as TOPvalue (see description of the WGM13:0 bitslocated in

theTCCR1A and theTCCR1B Register), the ICP1 isdisconnected andconsequently

theinput capture function isdisabled.

• Bit 5: Reserved Bit

Thisbit isreservedforfutureuse. For ensuring compatibilitywithfuture devices, thisbit

must be written to zero when TCCR1B iswritten.

• Bit 4:3 – WGM13:2: Waveform Generation Mode

See TCCR1A Registerdescription.

• Bit 2:0 – CS12:0: Clock Select

Thethree Clock Select bitsselectthe clock sourcetobeusedbytheTimer/Counter, see

Figure55andFigure56.

If externalpin modes areusedfor theTimer/Counter1, transitions on theT1pin will

clock the counter even if the pin isconfigured as an output. Thisfeatureallows software

control of the counting.

Timer/Counter1 – TCNT1H

and TCNT1L

Thetwo

Timer/Counter

I/Olocations(TCNT1H and TCNT1L, combined TCNT1) give

directaccess, bothforread andforwrite operations, to theTimer/Counter unit 16-bit

counter.Toensurethat both the high andlowbytes are read andwritten simultaneously

when the CPU accesses these registers, theaccess isperformed usingan8-bit tempo-

rary highbyte register(TEMP).This temporary register issharedbyall theother 16-bit

registers. See “Accessing 16-bit Registers”onpage 97.

Modifying the counter(TCNT1)whilethe counter isrunning introduces a risk of missing

a comparematch between TCNT1 and one of the OCR1x Registers.

Writing to theTCNT1 registerblocks (removes) the comparematch on the following

timerclock for all compare units.

Table 54. Clock Select Bit Description

CS12 CS11 CS10 Description

000No clock source (Timer/counterstopped).

001clk

I/O

/1 (No prescaling)

010clk

I/O

/8 (From prescaler)

011clk

I/O

/64 (From prescaler)

100clk

I/O

/256(From prescaler)

101clk

I/O

/1024 (From prescaler)

110Externalclock sourceonT1pin. Clock on falling edge.

111Externalclock sourceonT1pin. Clock on rising edge.

Bit 76543 210

TCNT1[15:8] TCNT1H

TCNT1[7:0] TCNT1L

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

Initial Value00000000

1 2 ... 114 115 116 117 118 119 120 121 122 123 124 ... 222 223

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