DS8005 Datasheet, PDF (12/20 Pages) Maxim Integrated Products – Smart Card Intergace

Smart Card Interface
4) V_{CC_} rises from 0 to 5V, 3V, or 1.8V with a controlled
slope (t₂ = t₁ + 1.5 × T). T is 64 times the internal
oscillator period (approximately 25µs).
5) I/O_ pin is enabled (t₃ = t₁ + 4T) (they were previ-
ously pulled low).
6) The CLK_ signal is applied to the C3 contact (t₄).
7) RST_ is enabled (t₅ = t₁ + 7T).
To apply the clock to the card interface:
1) Set RSTIN high.
2) Set CMDVCC low.
3) Set RSTIN low between t₃ and t₅; CLK_ now starts.
4) RST_ stays low until t₅, then RST becomes the copy
of RSTIN.
5) RSTIN has no further effect on CLK_ after t₅.
If the applied clock is not needed, set CMDVCC low
with RSTIN low. In this case, CLK_ starts at t₃ (minimum
200ns after the transition on I/O; see Figure 4); after t₅,
RSTIN can be set high to obtain an answer to request
(ATR) from an inserted smart card. Do not perform acti-
vation with RSTIN held permanently high.
Active Mode
When the activation sequence is completed, the card
interface is in active mode. The host microcontroller
and the smart card exchange data on the I/O lines.
Deactivation Sequence
When a session is completed, the host microcontroller
sets the CMDVCC line high to execute an automatic
deactivation sequence and returns the card interface to
the inactive mode (Figure 5).
1) RST_ goes low (t₁₀).
2) CLK_ is held low (t₁₂ = t₁₀ + 0.5 × T) where T is 64
times the period of the internal oscillator (approxi-
mately 25µs).
3) I/O_ pin is pulled low (t₁₃ = t₁₀ + T).
4) V_CC starts to fall (t₁₄ = t₁₀ + 1.5 × T).
5) When V_{CC_} reaches its inactive state, the deactiva-
tion sequence is complete (at t_DE).
6) All card contacts become low impedance to GND;
I/OIN remains at V_DD (pulled up through an 11kΩ
resistor).
7) The internal oscillator returns to its lower frequency.
V_CC Generator
Each V_{CC_} generator has a capacity to supply up to
80mA continuously at 5V, 65mA at 3V, and 30mA at
1.8V. An internal overload detector triggers at approxi-
mately 120mA. Current samples to the detector are fil-
tered. This allows spurious current pulses (with a
duration of a few µs) up to 200mA to be drawn without
causing deactivation. The average current must stay
below the specified maximum current value. To main-
tain V_CC voltage accuracy, a 100nF capacitor (with an
ESR < 100mΩ) should be connected to CGND and
placed near the V_{CC_} pin, and a 100nF or 220nF
capacitor (220nF is the best choice) with the same ESR
should be connected to CGND and placed near the
smart card reader’s C1 contact.
Fault Detection
The following fault conditions are monitored:
• Short-circuit or high current on V_{CC_}
• Removal of a card during a transaction
• V_DD dropping
• Card voltage generator operating out of the specified
values (V_DDA too low or current consumption too
high)
• Overheating
There are two different cases (Figure 6):
• CMDVCC High Outside a Card Session. Output
OFF_ is low if a card is not in the card reader and
high if a card is in the reader. The V_DD supply is mon-
itored—a decrease in input voltage generates an
internal power-on reset pulse but does not affect the
OFF_ signal. Short-circuit and temperature detection
is disabled because the card is not powered up.
• CMDVCC Low Within a Card Session. Output OFF_
goes low when a fault condition is detected, and an
emergency deactivation is performed automatically
(Figure 7). When the system controller resets CMD-
VCC to high, it may sense the OFF_ level again after
completing the deactivation sequence. This distin-
guishes between a card extraction and a hardware
problem (OFF_ goes high again if a card is present).
Depending on the connector’s card-present switch
(normally closed or normally open) and the mechani-
cal characteristics of the switch, bouncing can occur
on the PRES_ signals at card insertion or withdrawal.
The device has a debounce feature with an 8ms typical
duration (Figure 6). When a card is inserted, output
OFF_ goes high after the debounce time delay. When
the card is extracted, an automatic deactivation
sequence of the card is performed on the first true/false
transition on PRES_ and output OFF_ goes low.
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