ATmega88 datasheet(263/340 Pages) ATMEL

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7530H–AVR–02/09

ATmega48/88/168 Automotive

24. Boot Loader Support – Read-While-Write Self-Programming, ATmega88 and

ATmega168

In ATmega88 and ATmega168, the Boot Loader Support provides a real Read-While-Write

Self-Programming mechanism for downloading and uploading 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 code and write (program) that code into the Flash

memory, or read 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 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.

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 25-12 on page 284)

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 276 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 267. 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 267.

ATmega88 Datasheet(PDF) 263 Page - ATMEL Corporation

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