ATA8741 ATMEL Corporation, ATA8741 Datasheet - Page 118

• Manufacturer Part Number: ATA8741
• Manufacturer: ATMEL Corporation

21.8
118
Compare Match Output Unit
ATA8741
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.
shows a simplified schematic of the logic affected by the COM1x1:0 bit setting. The I/O Regis-
ters, 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 21-5. Compare Match Output Unit, 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
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. See
and
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
The COM1x1:0 bits have no effect on the Input Capture unit.
Table 21-3 on page 130
COMnx1
COMnx0
FOCnx
clk
I/O
“Register Description” on page 129
Waveform
Generator
for details.
D
D
D
PORT
DDR
OCnx
Table 21-1 on page
Q
Q
Q
1
0
129,
Figure 21-5 on page 118
Table 21-2 on page 129
9140B–INDCO–07/09
OCnx
Pin