ATmega16U4 datasheet(350/408 Pages) ATMEL

350 / 408 page

350

7766D–AVR–01/09

ATmega16U4/ATmega32U4

Note:

1. The SPIEN Fuse is not accessible in serial programming mode.

2. The default value of BOOTSZ1..0 results in maximum Boot Size. See Table 27-8 on page 346

for details.

3. See “Watchdog Timer” on page 54 for details.

4. Never ship a product with the OCDEN Fuse programmed regardless of the setting of Lock bits

and JTAGEN Fuse. A programmed OCDEN Fuse enables some parts of the clock system to

be running in all sleep modes. This may increase the power consumption.

Note:

1. The default value of SUT1..0 results in maximum start-up time for the default clock source.

See Table 8-1 on page 49 for details.

2. The default setting of CKSEL3..0 results in internal RC Oscillator @ 8 MHz. See Table 6-1 on

page 28 for details.

3. The CKOUT Fuse allow the system clock to be output on PORTC7. See “Clock Output Buffer”

on page 37 for details.

4. See “System Clock Prescaler” on page 37 for details.

The status of the Fuse bits is not affected by Chip Erase. Note that the Fuse bits are locked if

Lock bit1 (LB1) is programmed. Program the Fuse bits before programming the Lock bits.

Table 28-4.

Fuse High Byte

Bit No

Description

Default Value

OCDEN(4)

Enable OCD

1 (unprogrammed, OCD

disabled)

JTAGEN

Enable JTAG

0 (programmed, JTAG

enabled)

SPIEN(1)

Enable Serial Program and Data

Downloading

0 (programmed, SPI prog.

enabled)

WDTON(3)

Watchdog Timer always on

1 (unprogrammed)

EESAVE

EEPROM memory is preserved

through the Chip Erase

0 (programmed, EEPROM

preserved)

BOOTSZ1

Select Boot Size (see Table 28-7

for details)

0 (programmed)(2)

BOOTSZ0

Select Boot Size (see Table 28-7

for details)

0 (programmed)(2)

BOOTRST

Select Bootloader Address as

Reset Vector

1 (unprogrammed, Reset

vector @0x0000)

Table 28-5.

Fuse Low Byte

Bit No

Description

Default Value

CKDIV8(4)

Divide clock by 8

0 (programmed)

CKOUT(3)

Clock output

1 (unprogrammed)

SUT1

Select start-up time

1 (unprogrammed)(1)

SUT0

Select start-up time

0 (programmed)(1)

CKSEL3

Select Clock source

0 (programmed)(2)

CKSEL2

Select Clock source

0 (programmed)(2)

CKSEL1

Select Clock source

1 (unprogrammed)(2)

CKSEL0

Select Clock source

0 (programmed)(2)

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