7.6.1
RAMPZ – Extended Z-pointer Register for ELPM/SPM
Bit
7
6
5
4
3
2
1
0
RAMPZ7
RAMPZ6
RAMPZ5
RAMPZ4
RAMPZ3
RAMPZ2
RAMPZ1
RAMPZ0
0x3B (0x5B)
Read/Write
Initial Value
RAMPZ
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
0
0
0
0
0
0
0
0
For ELPM/SPM instructions, the Z-pointer is a concatenation of RAMPZ, ZH, and ZL, as shown
in Figure 7-4. Note that LPM is not affected by the RAMPZ setting.
Figure 7-4. The Z-pointer used by ELPM and SPM
Bit (
Individually)
7
0
7
0
8
7
7
0
0
RAMPZ
ZH
ZL
Bit (Z-pointer)
23
16
15
The actual number of bits is implementation dependent. Unused bits in an implementation will
always read as zero. For compatibility with future devices, be sure to write these bits to zero.
7.6.2
EIND – Extended Indirect Register
Bit
0x3C (0x5C)
7
6
EIND6
R/W
0
5
EIND5
R/W
0
4
EIND4
R/W
0
3
EIND3
R/W
0
2
EIND2
R/W
0
1
EIND1
R/W
0
0
EIND0
R/W
0
EIND7
EIND
Read/Write
R/W
Initial Value
0
For EICALL/EIJMP instructions, the Indirect-pointer to the subroutine/routine is a concatenation
of EIND, ZH, and ZL, as shown in Figure 7-5. Note that ICALL and IJMP are not affected by the
EIND setting.
Figure 7-5. The Indirect-pointer used by EICALL and EIJMP
Bit (Individual-
ly)
7
0
7
0
7
7
0
0
EIND
ZH
ZL
Bit (Indirect-
pointer)
23
16
15
8
The actual number of bits is implementation dependent. Unused bits in an implementation will
always read as zero. For compatibility with future devices, be sure to write these bits to zero.
7.7
Instruction Execution Timing
This section describes the general access timing concepts for instruction execution. The AVR
CPU is driven by the CPU clock clkCPU, directly generated from the selected clock source for the
chip. No internal clock division is used.
Figure 7-6 shows the parallel instruction fetches and instruction executions enabled by the Har-
vard architecture and the fast-access Register File concept. This is the basic pipelining concept
to obtain up to 1 MIPS per MHz with the corresponding unique results for functions per cost,
functions per clocks, and functions per power-unit.
16
ATmega640/1280/1281/2560/2561
2549L–AVR–08/07
ATMEL [ ATMEL ]
