AT90SCR100 datasheet(373/433 Pages) ATMEL

373 / 433 page

373

TPR0327AY–SMS–30Jan09

AT90SCR100

28.7.10

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 28-5 on page 373 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.

Note:

1. All other addresses are reserved for future use.

28.7.11

Preventing Flash Corruption

During periods of low VCC, 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.

Flash corruption can easily be avoided by following these design recommendations (one is

sufficient):

1. If there is no need for a Boot Loader update in the system, program the Boot Loader

Lock bits to prevent any Boot Loader software updates.

2. Keep the AVR RESET active (low) during periods of insufficient power supply voltage.

This can be done by enabling the internal Brown-out Detector (BOD) if the operating

voltage matches the detection level. If not, an external low VCC reset protection circuit

can be used. If a reset occurs while a write operation is in progress, the write operation

will be completed provided that the power supply voltage is sufficient.

Table 28-5.

Signature Row Addressing(1)

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 0

0x0006

Serial Number byte 1

0x0008

Serial Number byte 2

0x000A

Serial Number byte 3

0x000C

Serial Number byte 4

0x000E

Serial Number byte 5

0x0010

Serial Number byte 6

0x0012

Serial Number byte 7

0x0014

Serial Number byte 8

0x0016

AT90SCR100 Datasheet(PDF) 373 Page - ATMEL Corporation

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