Rainbow Electronics AT83C26 - Manual (Page 19)

19
7511B–SCR–10/05
AT83C26
Card Presence Detection
Card presence detection for SC1 interface
The card presence signal is connected on the CPRES1 pin. The polarity of card presence con-
tact is selected with the CARDDET1 bit (see SC1_CFG1 register). A programmable filtering is
controlled with the CDS1[2-0] bits.
The internal pull-up on the CPRES1 pin can be disconnected in order to reduce the consump-
tion. An external pull-up must be connected to Vcc. The PULLUP1 bit (see SC1_CFG1 register)
controls this feature.
Figure 12. SC1 presence Input
If the card presence contact is connected to Vcc, the internal pull-up must be disconnected and
an external pull-down must be connected to the CPRES1 pin.
An interrupt can be generated if a card is inserted or extracted (see Section “Interrupts”,
page 30).
Card Presence Detection for SC2 interface
Figure 13. SC2 presence Input
PULLUP1 Bit CARDDET1 Bit
= 1 Closed
= 0 Open
External
Pull-up
Resistor
Card
Presence
Contact
= 1 No Card if CPRES1 = 0
= 0 No Card if CPRES1 = 1
CARDIN1 bit
= 1 Card Inserted
= 0 No Card
CPRES1
INT
VCC
FILTERING
CDS1[2-0]
VCC
VSS
INT_PULLUP Bit
= 1 Closed
= 0 Open
VCC
External
Pull-down
Resistor
Card
Presence
Contact
VCC
VSS
PULLUP2 Bit CARDDET2 Bit
= 1 Closed
= 0 Open
External
Pull-up
Resistor
Card
Presence
Contact
= 1 No Card if CPRES2 = 0
= 0 No Card if CPRES2 = 1
CARDIN2 bit
= 1 Card Inserted
= 0 No Card
CPRES2
INT
VCC
FILTERING
CDS2[2-0]
VCC
VSS
INT_PULLUP Bit
= 1 Closed
= 0 Open
VCC
External
Pull-down
Resistor
Card
Presence
Contact
VCC
VSS
ITDIS2 Bit
= 0 Closed
= 1 Open