Rainbow-electronics ATmega128RFA1 Bedienungsanleitung PDF herunterladen (Seite 14)

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8266A-MCU Wireless-12/09

ATmega128RFA1

7.6.2 SPL – Stack Pointer Low

Bit 7 6 5 4 3 2 1 0

$3D ($5D) SP7 SP6 SP5 SP4 SP3 SP2 SP1 SP0 SPL

Read/Write RW RW RW RW RW RW RW RW

Initial Value 1 1 1 1 1 1 1 1

The AVR Stack Pointer is implemented as two 8-bit registers SPL and SPH in the I/O

space. The number of bits actually used is implementation dependent. Note that the

data space in some implementations of the AVR architecture is so small that only SPL

is needed. In this case, the SPH Register will not be present.

• Bit 7:0 – SP7:0 - Stack Pointer Low Byte

7.6.3 RAMPZ – Extended Z-pointer Register for ELPM/SPM

Bit 7 6 5 4 3 2 1 0

$3B ($5B) Res5 Res4 Res3 Res2 Res1 Res0 RAMPZ1

RAMPZ0

RAMPZ

Read/Write RW RW RW RW RW RW RW RW

Initial Value 0 0 0 0 0 0 0 0

For ELPM/SPM instructions, the Z-pointer is a concatenation of RAMPZ, ZH, and ZL.

Note that LPM is not affected by the RAMPZ setting.

• Bit 7:2 – Res5:0 - Reserved

For compatibility with future devices, be sure to write these bits to zero.

• Bit 1:0 – RAMPZ1:0 - Extended Z-Pointer Value

These two bits represent the MSB's of the Z-Pointer.

Table 7-2 RAMPZ Register Bits

RAMPZ1:0 0 Default value of Z-pointer MSB's.

For ELPM/SPM instructions, the Z-pointer is a concatenation of RAMPZ, ZH, and ZL,

as shown in Figure 7-3 below. Note that LPM is not affected by the RAMPZ setting.

Figure 7-3. The Z-pointer used by ELPM and SPM

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.

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