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Architectural
Overview
1004D–09/01
The fast-access register file concept contains 32 x 8-bit general-purpose working regis-
ters with a single clock cycle access time. This means that during one single clock cycle,
one ALU (Arithmetic Logic Unit) operation is executed. Two operands are output from
the register file, the operation is executed and the result is stored back in the register file
– in one clock cycle.
Six of the 32 registers can be used as three 16-bit indirect address register pointers for
Data Space addressing, enabling efficient address calculations. One of the three
address pointers is also used as the address pointer for the constant table look-up func-
tion. These added function registers are the 16-bit X-, Y-, and Z-register.
Figure 5. The AT90S2323/2343 AVR RISC Architecture
1K x 16
Program
Flash
Instruction
Register
Instruction
Decoder
Control Lines
The ALU supports arithmetic and logic functions between registers or between a con-
stant and a register. Single register operations are also executed in the ALU. Figure 5
shows the AT90S2323/2343 AVR RISC microcontroller architecture.
In addition to the register operation, the conventional memory addressing modes can be
used on the register file as well. This is enabled by the fact that the register file is
assigned the 32 lowermost Data Space addresses ($00 - $1F), allowing them to be
accessed as though they were ordinary memory locations.
The I/O memory space contains 64 addresses for CPU peripheral functions such as
Control Registers, Timer/Counters, A/D converters and other I/O functions. The I/O
memory can be accessed directly or as the Data Space locations following those of the
register file, $20 - $5F.
AT90S/LS2323/2343
Data Bus 8-bit
Program
Status
Counter
and Test
32 x 8
General
Purpose
Registers
ALU
128 x 8
Data
SRAM
Control
Registers
Interrupt
Unit
SPI
Unit
8-bit
Timer/Counter
Watchdog
Timer
I/O Lines
128 x 8
EEPROM
7
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