AT90SCR100 datasheet(363/433 Pages) ATMEL

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TPR0327AY–SMS–30Jan09

AT90SCR100

28. Boot Loader Support - Read-While-Write Self-Programming

The Boot Loader Support provides a real Read-While-Write Self-Programming mechanism to

download and upload program code by the MCU itself. This feature allows flexible application

software updates controlled by the MCU using a Flash-resident Boot Loader program. The Boot

Loader program can use any available data interface and associated protocol to read and/or

write (program) code into the Flash memory. The program code within the Boot Loader section

has the capability to write into the entire Flash, including the Boot Loader memory. Thus, the

Boot Loader can modify itself or erase itself from the code if the feature is not needed anymore.

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.

28.1

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 Size

• Code Efficient Algorithm

• Efficient Read-Modify-Write Support

28.2

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 28-2). The size of the different sections is configured by the

BOOTSZ Fuses as shown in Table 28-7 on page 376 and Figure 28-2. These two sections can

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

28.2.1

Application Section

The Application section is the section of the Flash that is used to store 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 28-2 on page 366. The Application section can never store any

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

section.

28.2.2

BLS – Boot Loader Section

While the Application section is used to store the application code, the The Boot Loader soft-

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

sequence 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 28-3 on page 366.

A page is a section in the Flash consisting of several bytes (see Table 29-7 on

page 381) used during programming sequence. The page organization does not

affect normal operation.

Note

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