AT90USB646-AU Datasheet, PDF (16/456 Pages) ATMEL Corporation – 8-bit Atmel Microcontroller with 64/128Kbytes of ISP Flash and USB Controller

5.6.1
RAMPZ - Extended Z-pointer register for ELPM/SPM
Bit
Read/write
Initial value
7
RAMPZ7
R/W
0
6
RAMPZ6
R/W
0
5
RAMPZ5
R/W
0
4
RAMPZ4
R/W
0
3
RAMPZ3
R/W
0
2
RAMPZ2
R/W
0
1
RAMPZ1
R/W
0
0
RAMPZ0
R/W
0
RAMPZ
For ELPM/SPM instructions, the Z-pointer is a concatenation of RAMPZ, ZH, and ZL, as shown
in Figure 5-4. Note that LPM is not affected by the RAMPZ setting.
Figure 5-4. The Z-pointer used by ELPM and SPM.
Bit (individually)
Bit (Z-pointer)
7
RAMPZ
23
0
7
ZH
16
15
0
7
0
ZL
8
7
0
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.
5.7 Instruction execution timing
This section describes the general access timing concepts for instruction execution. The AVR
CPU is driven by the CPU clock clk_CPU, directly generated from the selected clock source for the
chip. No internal clock division is used.
Figure 5-5 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.
Figure 5-5. The parallel instruction fetches and instruction executions.
T1
T2
T3
T4
clk_CPU
1st instruction fetch
1st instruction execute
2nd instruction fetch
2nd instruction execute
3rd instruction fetch
3rd instruction execute
4th instruction fetch
Figure 5-6 shows the internal timing concept for the Register File. In a single clock cycle an ALU
operation using two register operands is executed, and the result is stored back to the destina-
tion register.
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