Description:

Stores one byte indirect with or without displacement from a register to data space. For parts with SRAM, the data space consists of the register file, I/O memory and internal SRAM (and external SRAM if applicable). For parts without SRAM, the data space consists of the register file only. The EEPROM has a separate address space.

The data location is pointed to by the Z (16 bits) pointer register in the register file. Memory access is limited to the current data segment of 64K bytes. To access another data segment in devices with more than 64K bytes data space, the RAMPX, RAMPY, RAMPZ in register in the I/O area has to be changed.

The Z pointer register can either be left unchanged by the operation, or it can be post-incremented or pre-decremented. These features are especially suited for stack pointer usage of the Z pointer register, however because the Z pointer register can be used for indirect subroutine calls, indirect jumps and table lookup, it is often more convenient to use the X or Y pointer as a dedicated stack pointer. Note that only the low byte of the Z pointer is updated in devices with no more than 256 bytes data space. For such devices, the high byte of the pointer is not used by this instruction and can be used for other purposes. The RAMPZ register in the I/O area is updated in parts with more than 64K bytes data space or more than 64K bytes program memory, and the increment/decrement/displacement is added to the entire 24-bit address on such devices.

Not all variants of this instruction is available in all devices. Refer to the device specific instruction set summary.

The result of these combinations is undefined:

ST Z+, r30

ST Z+, r31

ST -Z, r30

ST -Z, r31

Using the Z pointer:

Operation: Comment:

(i) (Z) ←Rr Z: Unchanged

(ii) (Z) ← Rr Z ← Z+1 Z: Post incremented

(iii) Z ← Z - 1 (Z) ← Rr Z: Pre decremented

(iiii)* (Z+q) ← Rr Z: Unchanged, q: Displacement

Syntax: Operands: Program Counter:

(i) ST Z, Rr 0 ≤ r ≤ 31 PC ← PC + 1

(ii) ST Z+, Rr 0 ≤ r ≤ 31 PC ← PC + 1

(iii) ST -Z, Rr 0 ≤ r ≤ 31 PC ← PC + 1

(iiii)* STD Z+q, Rr 0 ≤ r ≤ 31, 0 ≤ q ≤ 63 PC ← PC + 1

Notes:

*)The displacement form of this instruction (LDD) is not available on AVR8L based devices.

16-bit Opcode :

(i)

1000

001r

rrrr

0000

(ii)

1001

001r

rrrr

0001

(iii)

1001

001r

rrrr

0010

(iiii)

10q0

qq1r

rrrr

0qqq

Status Register (SREG) and Boolean Formula:

I

T

H

S

V

N

Z

C

-

-

-

-

-

-

-

-

Example:

clr r31 ; Clear Z high byte
ldi r30,$60 ; Set Z low byte to $60
st Z+,r0 ; Store r0 in data space loc. $60(Z post inc)
st Z,r1 ; Store r1 in data space loc. $61
ldi r30,$63 ; Set Z low byte to $63
st Z,r2 ; Store r2 in data space loc. $63
st -Z,r3 ; Store r3 in data space loc. $62(Z pre dec)
std Z+2,r4 ; Store r4 in data space loc. $64

Words:1 (2 bytes)

Cycles:

 

Cycles

Cycles xmega

Cycles AVR8L

(i)

2

1

1

(ii)

2

1

1

(iii)

2

2

2

(iiii)

2

2

N/A