AT43USB325 datasheet(41/109 Pages) ATMEL

41 / 109 page

3355C–USB–4/05

AT43USB325

5.1.2

Stack Pointer Register – SP

The Stack Pointer points to the data SRAM stack area where the Subroutine and Interrupt

Stacks are located. This Stack space in the data SRAM must be defined by the program before

any subroutine calls are executed or interrupts are enabled. The stack pointer must be set to

point above $60. The Stack Pointer is decremented by one when data is pushed onto the Stack

with the PUSH instruction, and it is decremented by two when an address is pushed onto the

Stack with subroutine calls and interrupts. The Stack Pointer is incremented by one when data is

popped from the Stack with the POP instruction and it is incremented by two when an address is

popped from the Stack with return from subroutine RET or return from interrupt RETI.

5.2

Sleep Modes

To enter the sleep modes, the SE bit in MCUCR must be set (one) and a SLEEP instruction

must be executed. If an enabled interrupt occurs while the MCU is in a sleep mode, the MCU

awakes, executes the interrupt routine, and resumes execution from the instruction following

SLEEP. The contents of the register file, SRAM and I/O memory are unaltered. If a reset occurs

during sleep mode, the MCU wakes up and executes from the Reset vector.

5.2.1

Power Down Mode

When the SM bit is set (one), the SLEEP instruction forces the MCU into the Power Down Mode.

In this mode, the external oscillator is stopped, while the external interrupts continue operating.

Only an external reset, an external level interrupt on INT0 or INT1, can wake up the MCU.

Note that when a level triggered interrupt is used for wake-up from power down, the low level

must be held for a time longer than the reset delay time-out period t

TOUT. Otherwise, the MCU

will fail to wake up.

Bit

131211

$3E ($5E)

SPH

$3D ($5D)

SP7

SP6

SP5

SP4

SP3

SP2

SP1

SP0

SPL

Read/Write

R/W

Initial Value

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