Datasheet

Bit 7 6 5 4 3 2 1 0
Rd FHB7 FHB6 FHB5 FHB4 FHB3 FHB2 FHB1 FHB0
When reading the Extended Fuse byte (EFB), load 0x0002 in the Z-pointer. When an LPM instruction is
executed within three cycles after the SPMCSR.BLBSET and SPMCSR.SPMEN are set, the value of the
Extended Fuse byte (EFB) will be loaded in the destination register as shown below.
Bit 7 6 5 4 3 2 1 0
Rd
– – – – – EFB2 EFB1 EFB0
Fuse and Lock bits that are programmed read as '0'. Fuse and Lock bits that are unprogrammed, will read
as '1'.
Related Links
Fuse Bits on page 363
27.8.10. Reading the Signature Row from Software
To read the Signature Row from software, load the Z-pointer with the signature byte address given in the
following table and set the SIGRD and SPMEN bits in SPMCSR (SPMCSR.SIGRD and
SPMCSR.SPMEN). When an LPM instruction is executed within three CPU cycles after the
SPMCSR.SIGRD and SPMCSR.SPMEN are set, the signature byte value will be loaded in the destination
register. The SPMCSR.SIGRD and SPMCSR.SPMEN will auto-clear upon completion of reading the
Signature Row Lock bits or if no LPM instruction is executed within three CPU cycles. When
SPMCSR.SIGRD and SPMCSR.SPMEN are cleared, LPM will work as described in the Instruction set
Manual.
Table 27-5. 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
Serial Number Byte 1 0x000E
Serial Number Byte 0 0x000F
Serial Number Byte 3 0x0010
Serial Number Byte 2 0x0011
Serial Number Byte 5 0x0012
Serial Number Byte 4 0x0013
Serial Number Byte 6 0x0015
Serial Number Byte 7 0x0016
Serial Number Byte 8 0x0017
Note: All other addresses are reserved for future use.
Atmel ATmega644A [DATASHEET]
Atmel-42716C-ATmega644A_Datasheet_Complete-10/2016
354