ST7SCR datasheet(59/102 Pages) STMICROELECTRONICS

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ST7SCR

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SMARTCARD INTERFACE (Cont’d)

12.4.3.5 Card detection mechanism

The CRDDET bit in the CRDCR Register indicates

if the card presence detector (card switch) is open

or closed when a card is inserted. When the

CRDIRF bit of the CRDSR is set, it indicates that a

card is present.

To be able to power-on the smartcard, card pres-

ence is mandatory. Removing the smartcard will

automatically start the ISO7816-3 card deactiva-

tion sequence (see Section 12.4.3.6).

There is no hardware debouncing: The CRDIRF

bit changes whenever the level on the CRDDET

pin changes. The card switch can generate an in-

terrupt which can be used to wake up the device

from suspend mode and for software debouncing.

Three different cases can occur:

– The microcontroller is in run mode, waiting for

card insertion:

Card insertion generates an interrupt and the

CRDIRF bit in the CRDSR register is set. De-

bouncing is managed by software. After the time

required for debouncing, if the CRDIRF bit is set,

the CRDVCC bit in the CRDCR register is set by

software to apply the selected voltage to the

CRDVCC pin

– The microcontroller is in suspend mode and a

card is inserted:

The ST7 is woken up by the interrupt. The card

insertion is then handled in the same way as in

the previous case.

– The card is removed:

– The CRDIRF bit is reset without hardware de-

bouncing

– A Card Insertion/Removal interrupt is generat-

ed, (if enabled by the CRDIRM bit in the

MISCR2 register)

– The CRDVCC bit is immediately reset by

hardware, starting the card deactivation se-

quence.

Figure 32. Card detection block diagram

CRDDET

CRD

CRDSR

CARD INSERTION/REMOVAL

IRF

DET

CRDCR

CNF

CRD

MISCR2

IRM

Pull-up

EDGE DETECTOR

Interrupt Request

SMARTCARD INTERFACE (CRD)

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