ATMEGA8_14 Datasheet, PDF (86/331 Pages) ATMEL Corporation – High-performance, Low-power Atmel

Figure 36. Compare Match Output Unit, Schematic
ATmega8(L)
COMnx1
COMnx0
FOCnx
Waveform
Generator
DQ
1
OCnx
0
DQ
OCnx
Pin
PORT
DQ
clk_I/O
DDR
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
Register bit for the OC1x pin (DDR_OC1x) must be set as output before the OC1x value is visi-
ble on the pin. The port override function is generally independent of the Waveform Generation
mode, but there are some exceptions. Refer to Table 36 on page 96, Table 37 on page 96 and
Table 38 on page 97 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 oper-
ation. See “16-bit Timer/Counter Register Description” on page 96.
The COM1x1:0 bits have no effect on the Input Capture unit.
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