ATtiny48 datasheet(94/266 Pages) ATMEL

94 / 266 page

8008C–AVR–03/09

ATtiny48/88

12.8

Compare Match Output Unit

The Compare Output mode (COM1x1:0) bits have two functions. The Waveform Generator uses

the COM1x1:0 bits for defining the Output Compare (OC1x) state at the next compare match.

Secondly the COM1x1:0 bits control the OC1x pin output source. Figure 12-5 shows a simplified

schematic of the logic affected by the COM1x1:0 bit setting. The I/O Registers, I/O bits, and I/O

pins in the figure are shown in bold. Only the parts of the general I/O Port Control Registers

(DDR and PORT) that are affected by the COM1x1:0 bits are shown. When referring to the

OC1x state, the reference is for the internal OC1x Register, not the OC1x pin. If a system reset

occur, the OC1x Register is reset to “0”.

Figure 12-5. Compare Match Output Unit (non-PWM Mode), Schematic

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 out-

put) is still controlled by the Data Direction Register (DDR) for the port pin. The Data Direction

ble on the pin. The port override function is generally independent of the Waveform Generation

mode, but there are some exceptions. Refer to Table 12-2, Table 12-3 and Table 12-4 for

details.

The design of the Output Compare pin logic allows initialization of the OC1x state before the out-

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

operation. See “Register Description” on page 105.

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

PORT

DDR

OCnx

Waveform

Generator

COMnx1

COMnx0

FOCnx

clk

I/O

ATtiny48 Datasheet(PDF) 94 Page - ATMEL Corporation