ATmega16U4 datasheet(351/408 Pages) ATMEL

351 / 408 page

351

7766D–AVR–01/09

ATmega16U4/ATmega32U4

28.2.1

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.

28.3

Signature Bytes

All ATMEL microcontrollers have a three-byte signature code which identifies the device. This

code can be read in both serial and parallel mode, also when the device is locked. The three

bytes reside in a separate address space.

ATmega16U4 Signature Bytes:

0x000: 0x1E (indicates manufactured by ATMEL).

0x001: 0x94 (indicates 16KB Flash memory).

0x002: 0x88 (indicates ATmega16U4 device).

ATmega32U4 Signature Bytes:

0x000: 0x1E (indicates manufactured by ATMEL).

0x001: 0x95 (indicates 32KB Flash memory).

0x002: 0x87 (indicates ATmega32U4 device).

28.4

Calibration Byte

The ATmega16U4/ATmega32U4 has a byte calibration value for the internal RC Oscillator. This

byte resides in the high byte of address 0x000 in the signature address space. During reset, this

byte is automatically written into the OSCCAL Register to ensure correct frequency of the cali-

brated RC Oscillator.

28.5

Parallel Programming Parameters, Pin Mapping, and Commands

This section describes how to parallel program and verify Flash Program memory, EEPROM

Data memory, Memory Lock bits, and Fuse bits in the ATmega16U4/ATmega32U4. Pulses are

assumed to be at least 250 ns unless otherwise noted.

28.5.1

Signal Names

In this section, some pins of the ATmega16U4/ATmega32U4 are referenced by signal names

describing their functionality during parallel programming, see Figure 28-1 and Table 28-6. Pins

not described in the following table are referenced by pin names.

The XA1/XA0 pins determine the action executed when the XTAL1 pin is given a positive pulse.

The bit coding is shown in Table 28-9.

When pulsing WR or OE, the command loaded determines the action executed. The different

commands are shown in Table 28-10.

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