AT43USB353M datasheet(8/95 Pages) ATMEL

8 / 95 page

AT43USB353M

3307B–USB–4/04

SRAM Data

Memory

Table 5 summarizes how the AT43USB353M SRAM Memory is organized. The lower 1120

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 1024 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-increment. 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 1024 bytes of internal data

SRAM in the AT43USB353M 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 5 and Table 6 give an

overview of these registers.

Table 3. Functional Difference Between AT43USB355 and AT43USB353M

Function

AT43USB355

AT43USB353M

Port B

PB[0:7]

No Port B

Port D

PD[0:7]

PD[0:6]

Port F

PF[0:3]

No Port F

External Counter Input

Yes, T0 = PB0, T1 = PB1

No T0, T1

SPI

Yes

No SPI

Analog Reference Input

External

Internally connected to CEXTA

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