Rainbow Electronics AT90LS8535 - Manual (Page 11)

11
AT90S/LS8535
1041H–11/01
SRAM Data Memory Figure 8 shows how the AT90S8535 SRAM memory is organized.
Figure 8. SRAM Organization
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 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 63 address locations reached from the
base address given by the Y- or Z-registers.
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 512 bytes of internal
data SRAM in the AT90S8535 are all accessible through all these addressing modes.
See the next section for a detailed description of the different addressing modes.
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
$025E
$025F
...
Internal SRAM