ATMEGA2561V ATMEL [ATMEL Corporation], ATMEGA2561V Datasheet - Page 324

• Manufacturer Part Number: ATMEGA2561V
• Description: 8-bit Microcontroller with 64K/128K/256K Bytes In-System Programmable Flash
• Manufacturer: ATMEL [ATMEL Corporation]

RWW – Read-While-Write
Section
NRWW – No Read-While-Write
Section
Table 134. Read-While-Write Features
324
Which Section does the Z-pointer
Address during the Programming?
RWW Section
NRWW Section
ATmega640/1280/1281/2560/2561
•
Note that the user software can never read any code that is located inside the RWW
section during a Boot Loader software operation. The syntax “Read-While-Write sec-
tion” refers to which section that is being programmed (erased or written), not which
section that actually is being read during a Boot Loader software update.
If a Boot Loader software update is programming a page inside the RWW section, it is
possible to read code from the Flash, but only code that is located in the NRWW sec-
tion. During an on-going programming, the software must ensure that the RWW section
never is being read. If the user software is trying to read code that is located inside the
RWW section (i.e., by load program memory, call, or jump instructions or an interrupt)
during programming, the software might end up in an unknown state. To avoid this, the
interrupts should either be disabled or moved to the Boot Loader section. The Boot
Loader section is always located in the NRWW section. The RWW Section Busy bit
(RWWSB) in the Store Program Memory Control and Status Register (SPMCSR) will be
read as logical one as long as the RWW section is blocked for reading. After a program-
ming is completed, the RWWSB must be cleared by software before reading code
located in the RWW section. See “SPMCSR – Store Program Memory Control and Sta-
tus Register” on page 340. for details on how to clear RWWSB.
The code located in the NRWW section can be read when the Boot Loader software is
updating a page in the RWW section. When the Boot Loader code updates the NRWW
section, the CPU is halted during the entire Page Erase or Page Write operation.
Which Section can be
Read during Programming?
When erasing or writing a page located inside the NRWW section, the CPU is halted
during the entire operation.
NRWW Section
None
CPU Halted?
No
Yes
Read-While-Write
Supported?
Yes
No
2549K–AVR–01/07