ST8024

12/23

Table 20: Clock frequency selection; (note 1)

NOTE 1: The status of pins CLKDIV1 and CLKDIV2 must not be changed simultaneously; a delay of 10 ns minimum between changes is

needed; the minimum duration of any state of CLK is eight periods of XTAL1.

The frequency change is synchronous, which means that during transition no pulse is shorter than 45% of

the smallest period, and that the first and last clock pulses about the instant of change have the correct

width.

When changing the frequency dynamically, the change is effective for only eight periods of XTAL1 after

to 55% duty factor on pin CLK, the input signal on pin XTAL1 should have a duty factor of 48 to 52% and

transition times of less than 5% of the input signal period.

If a crystal is used, the duty factor on pin CLK may be 45 to 55% depending on the circuit layout and on

the crystal characteristics and frequency. In other cases, the duty factor on pin CLK is guaranteed

between 45 and 55% of the clock period.

The crystal oscillator runs as soon as the IC is powered up. If the crystal oscillator is used, or if the clock

pulse on pin XTAL1 is permanent, the clock pulse is applied to the card as shown in the activation

sequences shown in Figs 5 and 6.

If the signal applied to XTAL1 is controlled by the system microcontroller, the clock pulse will be applied

to the card when it is sent by the system microcontroller (after completion of the activation sequence).

I/O TRANSCEIVERS

The three data lines I/O, AUX1 and AUX2 are identical.The idle state is realized by both I/O and I/OUC

lines being pulled HIGH via a 11 k

transceiver to receive a falling edge becomes the master. An anti-latch circuit disables the detection of

transistor on the slave side is turned on, thus transmitting the logic 0 present on the master side. When the

then both sides return to their idle states. This active pull-up feature ensures fast LOW-to-HIGH

At the end of the active pull-up pulse, the output voltage depends only on the internal pull-up resistor and

the load current. The current to and from the card I/O lines is limited internally to 15 mA and the maximum

frequency on these lines is 1 MHz.

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 k

- Voltage generators are stopped

- XTAL oscillator is running

- Voltage supervisor is active

- The internal oscillator is running at its low frequency.

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 Table 21.

CLKDIV1

CLKDIV2

00

01

11

10