Datasheet
ST8024 Functional description
19/31
5.5 Inactive mode
After a power-on reset, the circuit enters the inactive mode. A minimum number of circuits
are active while waiting for the microcontroller to start a session:
– All card contacts are inactive (approximately 200 Ω to GND)
– Pins I/OUC, AUX1UC and AUX2UC are in the high-impedance state (11 kΩ pull-up
resistor to V
DD
)
– Voltage generators are stopped
– XTAL oscillator is running
– Voltage supervisor is active
– The internal oscillator is running at its low frequency.
5.6 Activation sequence
After power-on and after the internal pulse width delay, the system microcontroller can
check the presence of a card using the signals OFF
and CMDVCC as shown in Tabl e 2 2.
If the card is in the reader (this is the case if PRES
or PRES is active), the system
microcontroller can start a card session by pulling CMDVCC
LOW. The following sequence
then occurs (see Figure 6):
1. CMDVCC
is pulled LOW and the internal oscillator changes to its high frequency (t
0
).
2. The voltage doubler is started (between t
0
and t
1
).
3. V
CC
rises from 0 to 5 V (or 3 V) with a controlled slope (t
2
= t
1
+ 1.5 x T) where T is
64 times the period of the internal oscillator (approximately 25 µs).
4. I/O, AUX1 and AUX2 are enabled (t
3
= t
1
+ 4T) (these were pulled LOW until this
moment).
5. CLK is applied to the C3 contact of the card reader (t
4
).
6. RST is enabled (t
5
= t
1
+ 7T).
The clock may be applied to the card using the following sequence (see Figure 5):
1. Set RSTIN HIGH.
2. Set CMDVCC
LOW.
3. Reset RSTIN LOW between t
3
and t
5
; CLK will start at this moment.
4. RST remains LOW until t
5
, when RST is enabled to be the copy of RSTIN.
5. After t
5
, RSTIN has no further affect on CLK; this allows a precise count of CLK
pulses before toggling RST.
If the applied clock is not needed, then CMDVCC
may be set LOW with RSTIN LOW. In this
case, CLK will start at t
3
(minimum 200 ns after the transition on I/O), and after t
5
, RSTIN
may be set HIGH in order to obtain an Answer To Request (ATR) from the card.
Activation should not be performed with RSTIN held permanently HIGH
Table 22. Card presence indicator
OFF CMDVCC Indication
H H Card present
L H Card not present