Sram data memory – Rainbow Electronics AT90LS2343 User Manual

Page 11

AT90S/LS2323/2343

1004D–09/01

SRAM Data Memory

Figure 9 shows how the AT90S2323/2343 Data Memory is organized.

Figure 9. SRAM Organization

The 224 data memory locations address the Register file, I/O memory and the data
SRAM. The first 96 locations address the Register file + I/O memory, and the next 128
locations address the 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 address space.

The Indirect with Displacement mode features 63 address locations reached from the
base address given by the Y- and Z-register.

When using register indirect addressing modes with automatic pre-decrement and post-
increment, the address registers X, Y, and Z are used and decremented and
incremented.

The 32 general-purpose working registers, 64 I/O registers and the 128 bytes of data
SRAM in the AT90S2323/2343 are all directly accessible through all these addressing
modes.

Register File

Data Address Space

$00

$01

$02

…

R29

$1D

R30

$1E

R31

$1F

I/O Registers

$00

$20

$01

$21

$02

$22

…

$3D

$5D

$3E

$5E

$3F

$5F

Internal SRAM

$60

$61

$62

…

$DD

$DE

$DF