Rainbow Electronics AT86RF401 - Manual (Page 21)

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AT86RF401
1424D–RKE–09/02
SRAM Data Memory Figure 10 shows how the AT86RF401 SRAM memory is organized.
Figure 10. SRAM Organization
The lower 224 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 128 locations address the internal data SRAM.
The five different addressing modes for the data memory cover: Direct, Indirect with Dis-
placement, Indirect, Indirect with Pre-decrement, and Indirect with Post-increment. In
the register file, registers R26 to R31 feature the indirect addressing pointer registers.
The direct addressing reaches the entire data space.
The Indirect with Displacement mode features a 63 address locations reach from the
base address given by the Y or Z register.
When using register indirect addressing modes with automatic pre-decrement and post-
increment, the address registers X, Y and Z are decremented and incremented.
The 32 general-purpose working registers, 64 I/O registers and the 128 bytes of internal
data SRAM in the AT86RF401 are all accessible through all these addressing modes.
Program and Data
Addressing Modes The AT86RF401 AVR Enhanced RISC microcontroller supports powerful and efficient
addressing modes for access to the program memory (Flash) and data memory (SRAM,
Register File and I/O Memory). This section describes the different addressing modes
supported by the AVR architecture. In the figures, OP means the operation code part of
the instruction word. To simplify, not all figures show the exact location of the address-
ing bits.
Register File
R0
R1
R2
R29
R30
R31
I/O Registers
$00
$01
$02
...
$3D
$3E
$3F
...
$0000
$0001
$0002
$001D
$001E
$001F
$0020
$0021
$0022
...
$005D
$005E
$005F
...
Data Address Space
$0060
$0061
$00DE
$00DF
...
Internal SRAM