ATMEGA64L-8MI View Datasheet(PDF) - Atmel Corporation

Part Name

Description

Manufacturer

ATMEGA64L-8MI

8-bit AVR® Microcontroller with 64K Bytes In-System Programmable Flash

Atmel Corporation 

Figure 50. Compare Match Output Unit, Schematic

ATmega64(L)

COMnx1

COMnx0

FOCnx

Waveform

Generator

DQ

1

OCnx

0

DQ

OCnx

Pin

PORT

DQ

Compare Output Mode and

Waveform Generation

clkI/O

DDR

The general I/O port function is overridden by the Output Compare (OCnx) from the

Waveform Generator if either of the COMnx1:0 bits are set. However, the OCnx pin

direction (input or output) is still controlled by the Data Direction Register (DDR) for the

port pin. The Data Direction Register bit for the OCnx pin (DDR_OCnx) must be set as

output before the OCnx value is visible on the pin. The port override function is generally

independent of the Waveform Generation mode, but there are some exceptions. Refer

to Table 58, Table 59 and Table 60 for details.

The design of the Output Compare pin logic allows initialization of the OCnx state before

the output is enabled. Note that some COMnx1:0 bit settings are reserved for certain

modes of operation. See “16-bit Timer/Counter Register Description” on page 131.

The COMnx1:0 bits have no effect on the Input Capture unit.

The Waveform Generator uses the COMnx1:0 bits differently in Normal, CTC, and PWM

modes. For all modes, setting the COMnx1:0 = 0 tells the Waveform Generator that no

action on the OCnx Register is to be performed on the next Compare Match. For com-

pare output actions in the non-PWM modes refer to Table 58 on page 132. For fast

PWM mode refer to Table 59 on page 132, and for phase correct and phase and fre-

quency correct PWM refer to Table 60 on page 133.

A change of the COMnx1:0 bits state will have effect at the first Compare Match after

the bits are written. For non-PWM modes, the action can be forced to have immediate

effect by using the FOCnx strobe bits.

2490G–AVR–03/04

121

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