Datasheet

Rx space consists of 32 general purpose working 8-bit registers (R0-R31). These
registers have the shortest (fastest) access time, which allows single-cycle Arith-
metic Logic Unit (ALU) operation.
I/O Memory space contains addresses for CPU peripheral function, such as Control
registers, SPI, and other I/O functions.
Due to the complexity, some AVR microcontrollers with more peripherals have
Extended I/O memory, which occupies part of the internal SRAM. Extended I/O
memory is MCU dependent.
Storing data in I/O and Extended I/O memory is handled by the compiler only. Users
can not use this memory space for storing their data.
Internal SRAM (Data Memory) is used for temporarily storing and keeping interme-
diate results and variables (static link and dynamic link).
There are four memory type specifiers that can be used to refer to the data memo-
ry: rx, data, io, sfr i register.
Related topics: Accessing individual bits, SFRs, Memory type specifiers
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MIKROELEKTRONIKA - SOFTWARE AND HARDWARE SOLUTIONS FOR EMBEDDED WORLD
8051 Specifics
mikroBasic PRO for AVR
CHAPTER 4