Rainbow-electronics ATmega8515L Instrukcja Użytkownika Pobierz pdf (Strona 105)

105

ATmega8515(L)

2512A–AVR–04/02

Compare Match Output

Unit

The

Compare Output mode

(COM1x1:0)bitshave two functions.The Waveform Gener-

ator uses the COM1x1:0 bitsfordefining the Output Compare (OC1x) state at thenext

comparematch. Secondly the COM1x1:0 bitscontrol the OC1xpin output source. Fig-

ure50shows a simplified schematic of the logic affectedbythe COM1x1:0 bit setting.

The I/O Registers, I/Obits, andI/Opins in the figureare showninbold. Only the parts of

the generalI/Oport controlregisters (DDRand PORT) that areaffectedbythe

COM1x1:0 bits are shown. When referringtothe OC1xstate, the referenceisfor the

internalOC1x Register, not the OC1xpin. If a System Reset occur, the OC1x Register is

reset to “0”.

Figure 50. Compare Match Output Unit,Schematic

The generalI/Oport function is overridden by the Output Compare (OC1x) from the

Waveform Generator if either of the COM1x1:0 bits are set. However, the OC1xpin

direction (input or output) isstill controlledbythe

Data Direction Register

(DDR)for the

port pin. The Data Direction Registerbit for the OC1xpin (DDR_OC1x) must be set as

output beforethe OC1x value is visibleonthe pin. The portoverride function is generally

independent of the waveform generation mode,but thereare some exceptions.Refer to

Table50, Table51, and Table52fordetails.

The design of theoutput compare pin logic allows initialization of the OC1xstate before

theoutput is enabled. Note that some COM1x1:0 bit settings are reservedforcertain

modes of operation. See “16-bit Timer/Counter RegisterDescription” on page 116.

The COM1x1:0 bitshavenoeffectontheinput capture unit.

PORT

DDR

OCnx

Waveform

Generator

COMnx1

COMnx0

DATA BUS

FOCnx

clk

I/O

1 2 ... 100 101 102 103 104 105 106 107 108 109 110 ... 222 223

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Rainbow-electronics ATmega8515L Instrukcja Użytkownika Strona 105