Sleep mode

As a sleep mode (English sleep: "sleep") is called a power-saving standby mode in a microprocessor , in this by a special machine instruction (for example, mnemonics SLEEP or HALT is added). For example, the device in question can be operated longer with one battery or rechargeable battery charge due to the resulting power savings .

The advantage of sleep mode compared to switching a device off and on again is that the processor can continue at the point where the program was interrupted. Since the memory modules must also be supplied with voltage during sleep mode, either static CMOS memories are used or the internal RAM of the processor is used exclusively .

In sleep mode, the processor does not execute a program , but waits for an external signal, for example an interrupt from a keystroke, in order to continue working. As a rule, there are different levels of sleep mode with different residual power consumption. In the simplest case, only the program is stopped and the peripherals switched off, but not the oscillator . This means that you can continue working very quickly when the sleep mode is ended, but the oscillator continues to consume power in the idle phase. If the oscillator is also switched off, the power consumption can be reduced to extremely low values, especially with CMOS components, which is used, for example, in infrared remote controls or pocket calculators with months of battery operation. In these applications it is irrelevant that the oscillator first has to oscillate for a few milliseconds before the program starts again.

Before executing the sleep command, you can usually determine which interrupts should end the state. If all interrupts are blocked, the processor can only be restarted with a hardware reset .

An even lower power consumption than in the sleep mode of the processor can be achieved with an external circuit by separating the battery voltage with the aid of FET switches and a suitable circuit for starting up the processor.

In the case of portable PCs , the sleep mode of the x86 processor is used when the standby mode is switched to, whereas the power supply is completely disconnected in the so-called idle state .