AT43USB351M datasheet(7/101 Pages) ATMEL

7 / 101 page

AT43USB351M

3302E–USB–7/04

lowest Data Space addresses ($00 - $1 F), allowing them to be accessed as though they were

ordinary memory locations.

The I/O memory space contains 64 addresses for CPU peripheral functions as Control Regis-

ters, Timer/Counters, and other I/O functions. The I/O Memory can be accessed directly, or as

the Data Space locations following those of the register file, $20 - $5F.

The AVR uses a Harvard architecture concept – with separate memories and buses for pro-

gram and data. The program memory is executed with a single-level pipelining. While one

instruction is being executed, the next instruction is pre-fetched from the program memory.

This concept enables instructions to be executed in every clock cycle. The program memory is

a downloadable SRAM or a mask programmed ROM.

With the relative jump and call instructions, the whole 24K address space is directly accessed.

Most AVR instructions have a single 16-bit word format. Every program memory address con-

tains a 16- or 32-bit instruction.

During interrupts and subroutine calls, the return address Program Counter (PC) is stored on

the stack. The stack is effectively allocated in the general data SRAM, and consequently, the

stack size is only limited by the total SRAM size and the usage of the SRAM. All user pro-

grams must initialize the Stack Pointer (SP) in the reset routine (before subroutines or

interrupts are executed). The 10-bit SP is read/write accessible in the I/O space.

The 1-Kbyte data SRAM can be easily accessed through the five different addressing modes

supported in the AVR architecture.

The memory spaces in the AVR architecture are all linear and regular memory maps. A flexi-

ble interrupt module has its control registers in the I/O space with an additional global interrupt

enable bit in the status register. All interrupts have a separate interrupt vector in the interrupt

vector table at the beginning of the program memory. The interrupts have priority in accor-

dance with their interrupt vector position. The lower the interrupt vector address, the higher the

priority.

Development

Support

The AT43USB351M uses the same program and development tools as the AT43USB355 and

other Atmel AVR microcontrollers, including: C compilers, macro assemblers, program debug-

gers/simulators and in-circuit emulators. The AT43DK355 development kit is also available,

including firmware source code for the most common USB applications.

AT43USB351M Datasheet(PDF) 7 Page - ATMEL Corporation