DS8005 Datasheet, PDF (17/20 Pages) Maxim Integrated Products – Smart Card Intergace

Smart Card Interface
Switching A/B Interfaces
One of the device’s key features is the ability to man-
age two card slots at the same time. The multiplexing
control signal SEL_AB is used to determine which inter-
face is active for communication, though it is possible
to leave both interfaces powered at the same time.
When switching between interfaces, the device pre-
serves the state of control signals CLKDIV1, CLKDIV2,
1.8V, 5V/3V, CMDVCC, and RSTIN by latching the pin
states. This allows the now inactive interface to stay
powered while the other interface is activated for com-
munication, and it also allows for fast switching
between card interfaces without the need for a card
deactivation and activation sequence. After switching
SEL_AB, the control signals CLKDIV1, CLKDIV2, 1.8V,
5V/3V, CMDVCC, and RSTIN must not be changed for
78µs while the device latches the state of the pins for
the inactive interface. After the control signals are
latched, a 42µs window is provided to change the control
inputs.
Note that the behavior of the OFF and OFF2 pins is
dependent on the SEL_AB pin. OFF always refers to
the active interface, and OFF2 always reports events
on the inactive interface. This allows the device to
monitor for card insertion and removal on both inter-
faces simultaneously. See Figure 10 for details on the
behavior of the SEL_AB, OFF, and OFF2 pins with
regard to card presence.
1_8V, 5V/3V, CLKDIV1,
CLKDIV2, RST, I/O
SEL_AB
TRANSITION
SENSOR
DELAY
OFF
OFF2
TRANSPARENT
LATCH A
ENA
REG A
CLKA DIV
TRANSPARENT
LATCH B
ENA
1
0
1
0
REG B
CLKB DIV
SMART CARD
STATUS 1
SMART CARD
STATUS 2
DS8005
V_CCA
CLKA
RSTA, I/OA, GNDA
V_CCB
CLKB
RSTB, I/OB, GNDB
PRESA
PRESB
Figure 10. Switching A/B Interfaces
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