AT90PWM2 datasheet(266/365 Pages) ATMEL

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4317K–AVR–03/2013

AT90PWM2/3/2B/3B

the code from the program memory. The program code within the Boot Loader section has the

capability to write into the entire Flash, including the Boot Loader memory. The Boot Loader can

thus even modify itself, and it can also erase itself from the code if the feature is not needed any-

more. The size of the Boot Loader memory is configurable with fuses and the Boot Loader has

two separate sets of Boot Lock bits which can be set independently. This gives the user a

unique flexibility to select different levels of protection.

24.1

Boot Loader Features

• Read-While-Write Self-Programming

• Flexible Boot Memory Size

• High Security (Separate Boot Lock Bits for a Flexible Protection)

• Separate Fuse to Select Reset Vector

• Optimized Page(1) Size

• Code Efficient Algorithm

• Efficient Read-Modify-Write Support

Note:

1. A page is a section in the Flash consisting of several bytes (see Table 25-11 on page 286)

used during programming. The page organization does not affect normal operation.

24.2

Application and Boot Loader Flash Sections

The Flash memory is organized in two main sections, the Application section and the Boot

Loader section (see Figure 24-2). The size of the different sections is configured by the

BOOTSZ Fuses as shown in Table 24-6 on page 278 and Figure 24-2. These two sections can

have different level of protection since they have different sets of Lock bits.

24.2.1

Application Section

The Application section is the section of the Flash that is used for storing the application code.

The protection level for the Application section can be selected by the application Boot Lock bits

(Boot Lock bits 0), see Table 24-2 on page 270. The Application section can never store any

Boot Loader code since the SPM instruction is disabled when executed from the Application

section.

24.2.2

BLS – Boot Loader Section

While the Application section is used for storing the application code, the The Boot Loader soft-

ware must be located in the BLS since the SPM instruction can initiate a programming when

executing from the BLS only. The SPM instruction can access the entire Flash, including the

BLS itself. The protection level for the Boot Loader section can be selected by the Boot Loader

Lock bits (Boot Lock bits 1), see Table 24-3 on page 270.

24.3

Read-While-Write and No Read-While-Write Flash Sections

Whether the CPU supports Read-While-Write or if the CPU is halted during a Boot Loader soft-

ware update is dependent on which address that is being programmed. In addition to the two

sections that are configurable by the BOOTSZ Fuses as described above, the Flash is also

divided into two fixed sections, the Read-While-Write (RWW) section and the No Read-While-

Write (NRWW) section. The limit between the RWW- and NRWW sections is given in Table 24-

7 on page 278 and Figure 24-2 on page 269. The main difference between the two sections is:

•

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.

AT90PWM2 Datasheet(PDF) 266 Page - ATMEL Corporation

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