ATmega16 datasheet(246/357 Pages) ATMEL

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246

2466S–AVR–05/09

ATmega16(L)

Boot Loader

Support – Read-

While-Write

Self-

Programming

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 applica-

tion 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 mem-

ory. 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 differ-

ent levels of protection.

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 107 on page 262

)

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

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 125). The size of the different sections is configured by the BOOTSZ

Fuses as shown in Table 100 on page 257 and Figure 125. These two sections can have differ-

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

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 96 on page 249. The Application section can never store any Boot

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

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 97 on page 249.

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 101

on page 257 and Figure 125 on page 248. 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.

Note that the user software can never read any code that is located inside the RWW section dur-

ing a Boot Loader software operation. The syntax “Read-While-Write section” 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.

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