Rainbow Electronics AT83C24NDS - Manual (Page 10)

10
4234F–SCR–10/05
AT83C24
– over-current detection on CVCC
– VCARDERR bit set in CONFIG0 register (out of range voltage on CVCC or bit set by
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 presence switch is usually connected 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 PULLUP bit) and an external pull-down must be connected 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