17
4234G–SCR–01/07
AT83C24
Software Activation (DC/DC Started by Writing in VCARD[1:0] bits) and ART bit = 0
The activation sequence is controlled by software using TWI commands, depending on the
cards to support. For ISO 7816 cards, the following sequence can be applied:
1. Card Voltage is set by software to the required value (VCARD[1:0] bits in CONFIG0
register). This writing starts the DC/DC.
2. Wait of the end of the DC/DC init with a polling on VCARDOK bit (STATUS register)
or wait for PRES/INT to go Low if enabled (if IT_SEL bit = 0 in CONFIG4 register).
When VCARDOK bit is set (by hardware), CARDIO bit should be set by software.
3. CKSTOP, IODIS are programmed by software. CKSTOP bit is reset to have the
clock running. IODIS is reset to drive the I/O, C4, C8 pins and the CIO,CC4, CC8
pins according to each other.
4. CRST pin is controlled by software using CARDRST bit (see INTERFACE register).
Figure 13. Software activation without automatic control (ART bit = 0)
Note: It is assumed that initially VCARD[1:0], CARDCK, CARDIO and CARDRST bits are cleared,
CKSTOP and IODIS are set (those bits are further explained in the registers description)
Note: The user should check the AT83C24 status and possibly resume the activation sequence if one
TWI transfer is not acknowledged during the activation sequence.
CVCC
CRST
CCLK
CIO
2
4
3
1
ATR
