ATmega16U4 datasheet(171/408 Pages) ATMEL

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7766D–AVR–01/09

ATmega16U4/ATmega32U4

When this bit is set, the Waveform Generation Module works in enhanced mode: the compare

registers OCR4A/B/D can welcome one more accuracy bit, while the LSB determines on which

clock edge the Compare condition is signalled and the output pin level is updated.

• Bits 5:0 – OC4OE5:OC4OE0: Output Compare Override Enable Bits

These bits are the Output Compare Override Enable bits that are used to connect or disconnect

the Output Compare Pins in PWM6 Modes with an instant response on the corresponding Out-

put Compare Pins. The actual value from the port register will be visible on the port pin, when

the Output Compare Override Enable Bit is cleared. Table 15-20 shows the Output Compare

Override Enable Bits and their corresponding Output Compare pins.

15.12.6

TCNT4 – Timer/Counter4

This 8-bit register contains the value of Timer/Counter4.

The Timer/Counter4 is realized as a 10-bit up/down counter with read and write access. Due to

synchronization of the CPU, Timer/Counter4 data written into Timer/Counter4 is delayed by one

and half CPU clock cycles in synchronous mode and at most one CPU clock cycles for asyn-

chronous mode. When a 10-bit accuracy is preferred, special procedures must be followed for

accessing the 10-bit TCNT4 register via the 8-bit AVR data bus. These procedures are

described in section “Accessing 10-Bit Registers” on page 160. Alternatively the Timer/Counter4

can be used as an 8-bit Timer/Counter. Note that the Timer/Counter4 always starts counting up

after writing the TCNT4 register.

15.12.7

TC4H – Timer/Counter4 High Byte

The temporary Timer/Counter4 register is an 2-bit read/write register.

• Bits 7:3- Res: Reserved Bits

These bits are reserved bits in the ATmega16U4/ATmega32U4 and always reads as zero.

• Bits 2- TC410: Additional MSB bits for 11-bit accesses in Enhanced PWM mode

If 10-bit accuracy is used, the Timer/Counter4 High Byte Register (TC4H) is used for temporary

storing the MSB bits (TC49, TC48) of the 10-bit accesses. The same TC4H register is shared

between all 10-bit registers within the Timer/Counter4. Note that special procedures must be fol-

lowed when accessing the 10-bit TCNT4 register via the 8-bit AVR data bus. These procedures

are described in section “Accessing 10-Bit Registers” on page 160.

Table 15-20. Output Compare Override Enable Bits vs. Output Compare Pins

OC4OE0

OC4OE1

OC4OE2

OC4OE3

OC4OE4

OC4OE5

OC4A

(PC6)

OC4A

(PC7)

OC4B

(PB5)

OC4B

(PB6)

OC4D

(PD6)

OC4D

(PD7)

Bit

76543210

MSB

LSB

TCNT4

Read/Write

R/W

Initial value

00000000

Bit

76543210

-----

TC410

TC49

TC48

TC4H

Read/Write

RRRRRR

R/W

Initial value

00000000

ATmega16U4 Datasheet(PDF) 171 Page - ATMEL Corporation

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