MEGA128CAN Datasheet, PDF (312/413 Pages) ATMEL Corporation – Microcontroller WITH 128K BYTES OF ISP FLASH AND CAN CONTROLLER

• When erasing or writing a page located inside the RWW section, the NRWW section
can be read during the operation.
• When erasing or writing a page located inside the NRWW section, the CPU is halted
during the entire operation.
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.
RWW – Read-While-Write
Section
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 a call/jmp/lpm 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 programming is completed, the RWWSB must be
cleared by software before reading code located in the RWW section. See “Store Pro-
gram Memory Control and Status Register – SPMCSR” on page 316 for details on how
to clear RWWSB.
NRWW – No Read-While-Write The code located in the NRWW section can be read when the Boot Loader software is
Section
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.
Table 114. Read-While-Write Features
Which Section does the Z-
pointer Address During the
Programming?
Which Section Can
be Read During
Programming?
RWW Section
NRWW Section
NRWW Section
None
Is the CPU
Halted?
No
Yes
Read-While-Write
Supported?
Yes
No
312 AT90CAN128
4250E–CAN–12/04