Power consumption and wakeup time measurements and results

AN2857

24/31

Doc ID 15241 Rev 3

5.1.6

Conclusions

Power consumption depends on:

●

Supply voltage

●

Clock frequency

The results presented in this section, show that the functioning mode (run, wait, active halt

and halt) of the MCU impacts consumption and can greatly reduce it.

For active halt and halt mode, the user can choose which regulator to be used (MVR or

LPVR) and the Flash state (operating mode or power-down mode). Using the results

presented in Section 5.1: Power consumption measurements and results, consumption is

estimated as follows:

●

MVR: About 135 µA

●

Flash: About 60 µA

●

AWU + LSI: About 4 µA

5.2

Wakeup time measurements and results

Wakeup time measurements are taken in low-power modes. Results are given in Table 11 to

Table 14.

The wake-up time is measured from the interrupt event to the first instruction execution in

the interrupt routine. Figure 7 explains the wakeup time measurement.

Note:

In the STM8S and STM8A datasheets the wake-up time is not defined in the same way. it

does not include the fetch of the interrupt vector.

5.2.1

Measurement configuration

Hardware environment

The following hardware configuration is used to measure the MCU wakeup time: one pin of

the microcontroller is used as an interrupt input pin. Another pin is used as an output pin.

The CPU clock is outputted on the CLK_CCO pin. These three pins are monitored on an

oscilloscope.

Firmware description

The code starts with the MCU configuration. One pin (PB5) is configured as an input

interrupt. After configuration, the MCU switches into low-power mode. When an external

interrupt is triggered, the MCU wakes up, and executes the interrupt routine. The interrupt

routine causes a pin (PB1) to toggle.

Note:

The results given in this section take into account the interrupt latency times because they

include the time between the external event occurring and the first instruction of the interrupt

routine being executed.

The code executed in the interrupt routine is described below:

ld A,#$02

ld $5005,A

ld A,#$00

ld $5005,A