Rainbow-electronics Atmega169L Manuel d'utilisateur télécharger pdf (Page 105)

105

ATmega169V/L

2514A–AVR–08/02

Compare Match Output

Unit

The

Compare Output mode

(COM1x1:0) bits have two functions. The Waveform Gener-

ator 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. Fig-

ure 43 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 43. 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 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 55, Table 56 and Table 57 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 “16-bit Timer/Counter Register Description” on page 116.

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

PORT

DDR

OCnx

Waveform

Generator

COMnx1

COMnx0

DATA BU S

FOCnx

clk

I/O

1 2 ... 100 101 102 103 104 105 106 107 108 109 110 ... 316 317

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Rainbow-electronics Atmega169L Manuel d'utilisateur Page 105