ATmega32U2 datasheet(236/314 Pages) ATMEL

236 / 314 page

236

7799B–AVR–07/09

ATmega8U2/16U2/32U2

shown below. Refer to Table 25-4 on page 248 for detailed description and mapping of the Fuse

High byte.

When reading the Extended Fuse byte, load 0x0002 in the Z-pointer. When an (E)LPM instruc-

tion is executed within three cycles after the BLBSET and SPMEN bits are set in the SPMCSR,

the value of the Extended Fuse byte (EFB) will be loaded in the destination register as shown

below. Refer to Table 25-3 on page 247 for detailed description and mapping of the Extended

Fuse byte.

Fuse and Lock bits that are programmed, will be read as zero. Fuse and Lock bits that are

unprogrammed, will be read as one.

23.8.10

Reading the Signature Row from Software

To read the Signature Row from software, load the Z-pointer with the signature byte address

given in Table 23-6 on page 236 and set the SIGRD and SPMEN bits in SPMCSR. When an

LPM instruction is executed within three CPU cycles after the SIGRD and SPMEN bits are set in

SPMCSR, the signature byte value will be loaded in the destination register. The SIGRD and

SPMEN bits will auto-clear upon completion of reading the Signature Row Lock bits or if no LPM

instruction is executed within three CPU cycles. When SIGRD and SPMEN are cleared, LPM will

work as described in the Instruction set Manual

ATmega8U2/16U2/32U2 includes a unique 10 bytes serial number located in the signature row.

This unique serial number can be used as a USB serial number in the device enumeration pro-

cess. The pointer addresses to access this unique serial number are given in Table 23-6 on

page 236..

Note:

All other addresses are reserved for future use.

23.8.11

Preventing Flash Corruption

During periods of low V

CC, the Flash program can be corrupted because the supply voltage is

too low for the CPU and the Flash to operate properly. These issues are the same as for board

level systems using the Flash, and the same design solutions should be applied.

A Flash program corruption can be caused by two situations when the voltage is too low. First, a

regular write sequence to the Flash requires a minimum voltage to operate correctly. Secondly,

the CPU itself can execute instructions incorrectly, if the supply voltage for executing instructions

is too low.

Bit

7654

FHB7

FHB6

FHB5

FHB4

FHB3

FHB2

FHB1

FHB0

Bit

7654

––––

–

EFB2

EFB1

EFB0

Table 23-6.

Signature Row Addressing

Signature Byte

Z-Pointer Address

Device Signature Byte 1

0x0000

Device Signature Byte 2

0x0002

Device Signature Byte 3

0x0004

RC Oscillator Calibration Byte

0x0001

Unique Serial Number

From 0x000E to 0x0018

ATmega32U2 Datasheet(PDF) 236 Page - ATMEL Corporation

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