Datasheet

ManualsBrandsMicrochip ManualsAVR MicrocontrollersAVR RISC Microcontroller Flash 8KB PDIP 16MHz

121

122

123

124

125

126

127

128

129

130

Figure 21-5. Compare Match Output Unit, Schematic

PORT

DDR

D Q

OCnx

D Q

Waveform

Generator

COMnx[1]

COMnx[0]

DATA BUS

FOCnx

clk

I/O

The general I/O port function is overridden by the Output Compare (OC1x) from the waveform generator

if either of the COM1x1:0 bits are set. However, the OC1x 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 OC1x pin

(DDR_OC1x) must be set as output before the OC1x 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 21-2, Table 21-3 and Table 21-4 for details.

The design of the Output Compare Pin logic allows initialization of the OC1x state before the output is

enabled. Note that some COM1x1:0 bit settings are reserved for certain modes of operation. See

The COM1x1:0 bits have no effect on the Input Capture unit.

21.8.1 Compare Output Mode and Waveform Generation

The waveform generator uses the COM1x1:0 bits differently in normal, CTC, and PWM modes. For all

modes, setting the COM1x1:0 = 0 tells the waveform generator that no action on the OC1x Register is to

be performed on the next Compare Match. For compare output actions in the non-PWM modes refer to

Table 21-2. For fast PWM mode refer to Table 21-3, and for phase correct and phase and frequency

correct PWM refer to Table 21-4.

A change of the COM1x1:0 bits state will have effect at the first Compare Match after the bits are written.

For nonPWM modes, the action can be forced to have immediate effect by using the FOC1x strobe bits.

21.9 Modes of Operation

The mode of operation (i.e., the behavior of the Timer/Counter and the Output Compare pins) is defined

by the combination of the Waveform Generation mode (WGM13:0) and Compare Output mode

(COM1x1:0) bits. The Compare Output mode bits do not affect the counting sequence, while the

Waveform Generation mode bits do. The COM1x1:0 bits control whether the PWM output generated

should be inverted or not (inverted or non-inverted PWM). For non-PWM modes the COM1x1:0 bits

control whether the output should be set, cleared or toggle at a Compare Match. See Compare Match

Output Unit.

AVR 8-Bit Microcontroller

16-bit Timer/Counter1

Datasheet Complete

40001974A-page 125