AT83C24 ATMEL Corporation, AT83C24 Datasheet - Page 10

• Manufacturer Part Number: AT83C24
• Description: Smart Card Reader Interface with Power Management
• Manufacturer: ATMEL Corporation

Card Presence Detection
10
Figure 4. Card Presence Input
VCC
VCC
VSS
VSS
AT83C24
Card
Contact
Presence
Card
Contact
External
Pull-down
External
Pull-up
Presence
PRES/INT
CPRES
•
The card presence is provided by the CPRES pin. The polarity of card presence contact
is selected with the CARDDET bit (see CONFIG1 register). A programmable filtering is
controlled with the CDS[2-0] bits (see CONFIG1 register).
An internal pull-up on the CPRES pin can be disconnected in order to reduce the con-
sumption, an external pull-up must then be connected to VCC. The PULLUP bit (see
CONFIG1 register) controls this feature.
The card presence switch is usually connected to Vss (card present if CPRES=1). The
CARDDET bit must be set. The internal pull up can be connected.
If the card presence contact is connected to Vcc (card present if CPRES=0), the internal
pull-up must be disconnected (see PULLUP bit) and an external pull-down must be con-
nected to the CPRES pin.
An interrupt can be generated if a card is inserted or extracted (see interrupts §).
If IT_SEL= 1 (mandatory for NDS applications and for software compatibility with
existing devices) the PRES/INT output is High to indicate a card is present and none
of the following event has occured:
–
–
Internal
Pull-up
EVCC
over-current detection on CVCC
VCARDERR bit set in CONFIG0 register (out of range voltage on CVCC or
bit set by software)
(See Table 18)
VCC
INT_PULLUP Bit
= 1 Closed
= 0 Open
PULLUP Bit
IT Controller
= 1 Closed
= 0 Open
IT_SEL Bit
CARDDET Bit
= 1 No Card if CPRES = 0
= 0 No Card if CPRES = 1
FILTERING
CDS[2-0]
= 1 Card Inserted
= 0 No Card
CARDIN bit
4234E–SCR–09/04