Rainbow Electronics ATmega8HVD - Manual (Page 15)

15
8052B–AVR–09/08
ATmega4HVD/8HVD
7.3 SRAM Data Memory
Figure 7-2 shows how the ATmega4HVD/8HVD SRAM Memory is organized.
The ATmega4HVD/8HVD is a complex microcontroller with more peripheral units than can be
supported within the 64 locations reserved in the Opcode for the IN and OUT instructions. For
the Extended I/O space from 0x60 - 0xFF in SRAM, only the ST/STS/STD and LD/LDS/LDD
instructions can be used.
The lower 512 data memory locations address both the Register File, the I/O memory,
Extended I/O memory, and the internal data SRAM. The first 32 locations address the Regis-
ter File, the next 64 location the standard I/O memory, then 160 locations of Extended 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 Displace-
ment, 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 reaches 63 address locations 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 or incremented.
The 32 general purpose working registers, 64 I/O Registers, 160 Extended I/O Registers, and
the 512 bytes of internal data SRAM in the ATmega4HVD/8HVD are all accessible through all
these addressing modes. The Register File is described in
”General Purpose Register File” on
page 9 .
Figure 7-2. Data Memory Map
7.3.1 Data Memory Access Times
This section describes the general access timing concepts for internal memory access. The
internal data SRAM access is performed in two clk
CPU
cycles as described in Figure 1 .
32 Registers
64 I/O Registers
Internal SRAM
(512 x 8)
0x0000 - 0x001F
0x0020 - 0x005F
0x02FF
0x0060 - 0x00FF
Data Memory
160 Ext I/O Reg.
0x0100