AN3985 datasheet(91/105 Pages) STMICROELECTRONICS

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AN3985

Application example

Doc ID 022255 Rev 2

91/105

Table 148 sums up the three low power modes available in this application example.

In each case, both CR95HF and STM8L devices are turned into low power state and the Tag

detection states are activated. The difference between the three states is the second source

of the system wake-up. It can be issued either by CR95HF or by STM8L.

Mode#1: Wait For Interrupt mode

In this state, the CPU of the STM8L is deactivated. An RTC interrupt is sent every 5 seconds

to STM8L. If the CR95HF has not seen a tag during 5 seconds, the STM8L's RTC clock

wakes up the MCU which sends an Interrupt to wake up the CR95HF. Then the

communication between CR95HF and STM8L is tested and the CR95HF is turned into Idle

state again before the STM8L returns into Wait For Interrupt mode. Figure 7 schematizes

these actions.

Figure 7.

Wait for interrupt mode schematic

Table 148.

Low power modes descriptions

Mode

Periodical

wake-up

STML8

CR95HF

Low power mode

Wake-up source

Low power mode

Wake-up source

1STM8L

Wait For Interrupt

– Internal RTC clock

– CR95HF

Tag Detection

– Tag Detection

–STM8L

CR95HF

Halt

CR95HF

Tag Detection

CR95HF

Halt

CR95HF

– Tag Detection

–Timer

– Tag Detection

– Internal Timer

MS19963V1

CR95HF

(1) Contactless tag

into operating

volume

2) STM8L send an pulse to

wake up CR95HF

1) internal timer

wakes up STM8L

3) A tag is detected, CR95HF

sent a pulse to wake up STM8L

2) A tag is detected,

CR95HF will wake up

STM8L

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