AT43USB325 datasheet(12/109 Pages) ATMEL

12 / 109 page

3355C–USB–4/05

AT43USB325

3.5

SRAM Data Memory

Table 3-3 summarizes how the AT43USB325 SRAM Memory is organized. The lower 608 Data

Memory locations address the Register file, the I/O Memory and the internal data SRAM. The

first 96 locations address the Register File + I/O Memory, and the next 512 locations address the

internal data SRAM. The five different addressing modes for the data memory cover: Direct,

Indirect with Displacement, Indirect, Indirect with Pre-decrement and Indirect with Post-incre-

ment. In the register file, registers R26 to R31 feature the indirect addressing pointer registers.

Direct addressing reaches the entire data space.

The Indirect with Displacement mode features 63 address locations that reach from the base

address given by the Y- or Z-register.

When using register indirect addressing modes with automatic pre-decrement and post-incre-

ment, the address registers X, Y, and Z are decremented and incremented.

The 32 general-purpose working registers, 64 I/O registers and the 512 bytes of internal data

SRAM in the AT43USB325 are all accessible through these addressing modes.

To manage the USB hardware, a special set of registers is assigned. These registers are

mapped to SRAM space between addresses $1F00 and 1FFF. Table 3-3 and Table 3-4 give an

overview of these registers.

AT43USB325 Datasheet(PDF) 12 Page - ATMEL Corporation