ATmega88PA Automotive Atmel Corporation, ATmega88PA Automotive Datasheet - Page 122

• Manufacturer Part Number: ATmega88PA Automotive
• Manufacturer: Atmel Corporation

16.8
122
Compare Match Output Unit
Atmel ATmega48PA/88PA/168PA [Preliminary]
Be aware that the COM1x1:0 bits are not double buffered together with the compare value.
Changing the COM1x1:0 bits will take effect immediately.
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.
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 sys-
tem reset occur, the OC1x Register is reset to “0”.
Figure 16-5. 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
output) is still controlled by the Data Direction Register (DDR) for the port pin. The Data Direc-
tion 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 Gener-
ation mode, but there are some exceptions. Refer to
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.
The COM1x1:0 bits have no effect on the Input Capture unit.
COMnx1
COMnx0
FOCnx
clk
I/O
See “Register Description” on page 133.
Waveform
Generator
D
D
D
PORT
DDR
OCnx
Q
Q
Q
Table
16-1,
1
0
Table 16-2
Figure 16-5
and
9223B–AVR–09/11
OCnx
Pin
Table 16-3
shows a