10
8210C–AVR–09/11
Atmel AVR XMEGA D
Figure 3-5.
The X-, Y- and Z-registers
.
The lowest register address holds the least-significant byte (LSB), and the highest register
address holds the most-significant byte (MSB). In the different addressing modes, these address
registers function as fixed displacement, automatic increment, and automatic decrement (see
the instruction set reference for details).
3.10
RAMP and Extended Indirect Registers
In order to access program memory above 64KB, the address pointer must be larger than 16
bits. This is done by concatenating one register to the Z-register. This register then holds the
most-significant byte (MSB) in a 24-bit address or address pointer.
These registers are available only on devices with external bus interface and/or more than 64KB
of program or data memory space. For these devices, only the number of bits required to
address the whole program and data memory space in the device is implemented in the
registers.
3.10.1
RAMPZ Registers
The RAMPZ registers are concatenated with the X-, Y-, and Z-registers, respectively, to enable
indirect addressing of the whole data memory space above 64KB and up to 16MB.
Figure 3-6.
The combined RAMPZ + Z registers.
When reading (ELPM) and writing (SPM) program memory locations above the first 128KB of
the program memory, RAMPZ is concatenated with the Z-register to form the 24-bit address.
LPM is not affected by the RAMPZ setting.
3.10.2
EIND - Extended Indirect Register
EIND is concatenated with the Z-register to enable indirect jump and call to locations above the
first 128KB (64K words) of the program memory.
Figure 3-7.
The combined EIND + Z register.
Bit (individually)
7
R27
0
7
R26
0
X-register
XH
XL
Bit (X-register)
15
8
7
0
Bit (individually)
7
R29
0
7
R28
0
Y-register
YH
YL
Bit (Y-register)
15
8
7
0
Bit (individually)
7
R31
0
7
R30
0
Z-register
ZH
ZL
Bit (Z-register)
15
8
7
0
Bit (Individually)
7
0
7
0
7
0
RAMPZ
ZH
ZL
Bit (Z-pointer)
23
16
15
8
7
0
Bit (Individually)
7
0
7
0
7
0
EIND
ZH
ZL
Bit (D-pointer)
23
16
15
8
7
0