Rainbow Electronics AT83C24NDS - Manual (Page 21)

21
4234F–SCR–10/05
AT83C24
Table 7. CONFIG 1 (Config Byte 1)
7 6 5 4 3 2 1 0
X ART SHUTDOWN CARDDET PULLUP CDS2 CDS1 CDS0
Bit
Number
Bit
Mnemonic Description
7 X This bit should not be set.
6 ART
Automatic Reset Transition
Set this bit to have the CRST pin changed according to activation sequence.
Clear this bit to have the CRST pin immediately following the value programmed
in CARDRST.
The reset value is 0.
5 SHUTDOWN
Shutdown
Set this bit to reduce the power consumption. An automatic de-activation
sequence will be done.
Clear this bit to enable VCARD[1:0] selection.
The reset value is 0.
4 CARDDET
Card Presence Detection Polarity
Set this bit to indicate the card presence detector is closed when no card is
inserted (CPRES is low).
Clear this bit to indicate the card presence detector is open when no card is
inserted (CPRES is high).Changing CARDDET will set INSERT bit (see
CONFIG0) even if no card is inserted or extracted.
The reset value is 0.
3 PULLUP
Pull-up Enable
Set this bit to enable the internal pull-up on the CPRES pin. This allows to
minimize the number of external components.
Clear this bit to disable the internal pull-up and minimize the power consumption
when the card detection contact is on. Then an external pull-up must be
connected to V
CC
(typically a 1 M Ω resistor).
The reset value is 1.
2-0 CDS[2:0]
Card Detection filtering
CPRES is sampled by the master clock provided on CLK input. A change on
CPRES is detected after:
CDS[2-0] = 0: 0 sample (1)
CDS[2-0] = 1: 4 identical samples
CDS [2-0] = 2: 8 identical samples (reset value)
CDS[2-0] = 3: 16 identical samples
CDS[2-0] = 4: 32 identical samples
CDS[2-0] = 5: 64 identical samples
CDS[2-0] = 6: 128 identical samples
CDS[2-0] = 7: 256 identical samples
The reset value is 2.
Note: When CDS[2-0] = 0 and IT_SEL = 0, PRES/INT = 1 when no
card is present and PRES/INT = 0 when a card is inserted
even if CLK is STOPPED. This can be used to wake up the
external microcontroller and restart CLK when a card is
inserted in the AT83C24.
If CDS[2-0] = 0, IT_SEL = 1 and CLK is stopped, a card insertion or
extraction has no effect on PRES/INT pin.