Low power modes

AN3404

12/30

Doc ID 018847 Rev 3

Figure 2.

STM8TL5xxx architecture

1.

Legend: I-Bus = instruction bus, D-Bus = databus, SWIM = single wire interface module; ITC = interrupt

controller

4.6

Wait mode

The STM8TL5xxx devices support two different Wait modes: Wait for interrupt (WFI) and

Wait for event (WFE). Both modes are designed to reduce STM8TL5xxx device power

consumption by switching off the core when it is not used. Wait mode is mainly used when

the STM8TL5xxx is waiting for an external or internal event so that the program execution

can continue.

The polling loop on an associated peripheral flag can be efficiently replaced by a wait

instruction (WFI() or WFE()) after having correctly configured the interrupt related to this flag

or the event in the WFE register.

Wait mode can be combined with peripheral clock gating and a low-speed clock source to

further reduce the power consumption of the device.

Wait mode also offers the lowest wakeup time which is interesting for applications

requesting a fast response time.

4.6.1

Entering Wait mode

Wait mode is entered by executing the WFI or WFE assembly instruction. This stops the

CPU, but other peripherals and the interrupt controller can continue to run. When entering

Wait mode, the global interrupts are automatically enabled.

●

Before entering WFI mode, at least one interrupt must be enabled.

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Before entering WFE mode, at least one event source must be enabled.