ATmega644PA datasheet(285/468 Pages) ATMEL

285 / 468 page

285

8152G–AVR–11/09

ATmega164PA/324PA/644PA/1284P

The page address must be written to PCPAGE. Other bits in the Z-pointer must be written to

zero during this operation.

• Page Write to the RWW section: The NRWW section can be read during the Page Write.

• Page Write to the NRWW section: The CPU is halted during the operation.

25.8.4

Using the SPM Interrupt

If the SPM interrupt is enabled, the SPM interrupt will generate a constant interrupt when the

SPMEN bit in SPMCSR is cleared. This means that the interrupt can be used instead of polling

the SPMCSR Register in software. When using the SPM interrupt, the Interrupt Vectors should

be moved to the BLS section to avoid that an interrupt is accessing the RWW section when it is

blocked for reading. How to move the interrupts is described in ”Interrupts” on page 62.

25.8.5

Consideration While Updating BLS

Special care must be taken if the user allows the Boot Loader section to be updated by leaving

Boot Lock bit11 unprogrammed. An accidental write to the Boot Loader itself can corrupt the

entire Boot Loader, and further software updates might be impossible. If it is not necessary to

change the Boot Loader software itself, it is recommended to program the Boot Lock bit11 to

protect the Boot Loader software from any internal software changes.

25.8.6

Prevent Reading the RWW Section During Self-Programming

During Self-Programming (either Page Erase or Page Write), the RWW section is always

blocked for reading. The user software itself must prevent that this section is addressed during

the self programming operation. The RWWSB in the SPMCSR will be set as long as the RWW

section is busy. During Self-Programming the Interrupt Vector table should be moved to the BLS

as described in ”Interrupts” on page 62, or the interrupts must be disabled. Before addressing

the RWW section after the programming is completed, the user software must clear the

RWWSB by writing the RWWSRE. See ”Simple Assembly Code Example for a Boot Loader” on

page 288 for an example.

25.8.7

Setting the Boot Loader Lock Bits by SPM

To set the Boot Loader Lock bits and general lock bits, write the desired data to R0, write

“X0001001” to SPMCSR and execute SPM within four clock cycles after writing SPMCSR.

See Table 25-2 and Table 25-3 for how the different settings of the Boot Loader bits affect the

Flash access.

If bits 5..0 in R0 are cleared (zero), the corresponding Boot Lock bit will be programmed if an

SPM instruction is executed within four cycles after BLBSET and SPMEN are set in SPMCSR.

The Z-pointer is don’t care during this operation, but for future compatibility it is recommended to

load the Z-pointer with 0x0001 (same as used for reading the lO

ck bits). For future compatibility it

is also recommended to set bits 7 and 6 in R0 to “1” when writing the Lock bits. When program-

ming the Lock bits the entire Flash can be read during the operation.

25.8.8

EEPROM Write Prevents Writing to SPMCSR

Note that an EEPROM write operation will block all software programming to Flash. Reading the

Fuses and Lock bits from software will also be prevented during the EEPROM write operation. It

Bit

765

432

BLB12

BLB11

BLB02

BLB01

LB2

LB1

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