The registers R26...R31 have some added functions to their general purpose usage. These registers are 16-bit address pointers for indirect addressing of the data space. The three indirect address registers X, Y, and Z are defined as described in the figure.
Figure 1. The
X-, Y-, and Z-registers
In the different addressing modes, these address registers have functions as fixed displacement, automatic increment, and automatic decrement (see the instruction set reference for details).