User Manual

10
4234F–SCR–10/05
AT83C24
– over-current detection on CVCC
– VCARDERR bit set in CONFIG0 re gister (out of rang e volt age on CVCC or bit set b y
software)
Card Presence Detection
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 consumption,
an external pull-up must then be connected to VCC. The PULLUP bit (see CONFIG1 register)
controls this feature.
The card prese nce switch is usually co nnected to Vss (card present if CPRES=1 ). The CARD-
DET 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 PULL UP bit) and an external pull-down must be connec ted to the
CPRES pin.
An interrupt can be generated if a card is inserted or extracted (see interrupts §).
Figure 4. Card Presence Input
PULLUP Bit CARDDET Bit
= 1 Closed
= 0 Open
= 1 No Card if CPRES = 0
= 0 No Card if CPRES = 1
CARDIN bit
= 1 Card Inserted
= 0 No Card
IT Controller
CPRES
PRES/INT
FILTERING
CDS[2-0]
VCC
INT_PULLUP Bit
= 1 Closed
= 0 Open
EVCC
IT_SEL Bit
(See Table 18)
Card
Presence
Contact
VCC
VCC
Card
Presence
Contact
VSS
VSS
External
Pull-up
External
Pull-down
Internal
Pull-up