AT90S8414
Preliminary
4-13
THE X-REGISTER, Y-REGISTER AND Z-REGISTER
The registers R26..R31 have some added functions to their general purpose usage. These registers are address pointers for
indirect addressing of the SRAM. The three indirect address registers X, Y and Z are defined as:
15
0
X - register
7 0
7 0
R27 ($1B)
R26 ($1A)
15
0
Y - register
7 0
7 0
R29 ($1D)
R28 ($1C)
15
0
Z - register
7 0
7 0
R31 ($1F)
R30 ($1E)
Figure 6: The X, Y and Z Registers
In the different addressing modes these address registers have functions as fixed displacement, automatic increment and
decrement (see the descriptions for the different instructions).
The ALU - Arithmetic Logic Unit
The high-performance
AVR
ALU operates in direct connection with all the 32 general purpose working registers. Within
a single clock cycle, ALU operations between registers in the register file are executed. The ALU operations are divided
into three main categories - arithmetic, logic and bit-functions. Some microcontrollers in the
AVR
product family feature
a hardware multiplier in the arithmetic part of the ALU.
The Downloadable Flash Program Memory
The AT90S8414 contains 8K bytes on-chip downloadable Flash memory for program storage. Since all instructions are
single 16-bit words, the Flash is organized as 4K x 16 words. The Flash memory has an endurance of at least 1000
write/erase cycles.
See Page 4-74 for a detailed description on Flash data downloading.
Constant tables must be allocated within the address 0-4K (see the LPM - Load Program Memory instruction
description).
See Page 4-15 for the different program memory addressing modes.
