ATMEGA640 datasheet(327/436 Pages) MICROCHIP

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327

ATmega640/V-1280/V-1281/V-2560/V-2561/V [DATASHEET]

DS40002211A

Notes: 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 29-7 on page 320 for details.

3. See “WDTCSR – Watchdog Timer Control Register” on page 65 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.

Notes: 1. The default value of SUT1:0 results in maximum start-up time for the default clock source. See “System and Reset

Characteristics” on page 360 for details.

2. The default setting of CKSEL3:0 results in internal RC Oscillator @ 8MHz. See Table 10-1 on page 40 for details.

3. The CKOUT Fuse allow the system clock to be output on PORTE7. See “Clock Output Buffer” on page 47 for

details.

4. See “System Clock Prescaler” on page 47 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.

30.2.1

Latching of Fuses

The fuse values are latched when the device enters programming mode and changes of the fuse values will have

no effect until the part leaves Programming mode. This does not apply to the EESAVE Fuse which will take effect

once it is programmed. The fuses are also latched on Power-up in Normal mode.

Table 30-4.

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

1 (unprogrammed, EEPROM not

preserved)

BOOTSZ1

Select Boot Size (see Table 30-9 on page 329 for

details)

0 (programmed)(2)

BOOTSZ0

Select Boot Size (see Table 30-9 on page 329 for

details)

0 (programmed)(2)

BOOTRST

Select Reset Vector

1 (unprogrammed)

Table 30-5.

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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