LTC1955 Linear Technology, LTC1955 Datasheet - Page 10

• Manufacturer Part Number: LTC1955
• Description: Dual Smart Card Interface
• Manufacturer: Linear Technology

LTC1955
OPERATIO
Table 1. Serial Port Commands
CARD B
CARD A
Table 2. V
D9
D1
0
0
1
1
Table 3. Clock Options
D7
D15
0
0
0
0
1
1
1
1
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D8
D0
0
1
0
1
D14
D6
0
0
1
1
0
0
1
1
CC
STATUS OUTPUT
0
0
0
0
Card B Electrical Fault
Card B ATR Fault
Card B V
Card B Present
0
0
0
0
Card A Electrical Fault
Card A ATR Fault
Card A V
Card A Present
Status (Card A)
Status (Card B)
V
V
V
V
and Shutdown Options
CC
CC
CC
CC
D13
= 0V (Shutdown)
= 1.8V
= 3V
= 5V
D5
0
1
0
1
0
1
0
1
CC
CC
U
Ready
Ready
Clock Mode Card B
Clock Mode Card A
Synchronous Mode
Unused
Asynchronous Stop Low
Asynchronous Stop High
Asynchronous 1
Asynchronous 2
Asynchronous 4
Asynchronous 8
D10 Card A Select/Deselect
D11 Card A Communications
D12 Options (See Table 4)
D13 Card A Clock Options
D14 (See Table 3)
D15
BIT COMMAND INPUT
D0
D1
D2
D3
D4
D5
D6
D7
D8
D9
V
(See Table 2)
Card B Select/Deselect
Data Pull-Up Defeat
Reserved (Always Set to “0”)
Card B Clock Options
(See Table 3)
V
(See Table 2)
CCB
CCA
Options
Options
To receive status data from the serial port, a read/write
operation must be performed. When polling for the pres-
ence of a smart card on both channels, the input word
should be set to $0000 since this is the shutdown com-
mand for the LTC1955. However, consider the example
where some operation is already being performed on
channel A. If, for example, the previous command was
$BE00 (V
DATA and CLK A set to ASYNC 2), then the commands for
this channel must be rewritten to the serial port each time.
To poll for the presence of a card on channel B, or even the
V
each new read/write cycle. Once a card is detected on
channel B, the commands for channel B can be changed
but the $BExx should continue to be rewritten for channel
A.
Bidirectional Channels
The bidirectional channels are level shifted to the appropri-
ate V
An NMOS pass transistor performs the level shifting. The
gate of the NMOS transistor is biased such that the
transistor is completely off when both sides have relin-
quished the channel. If one side of the channel asserts an
L, then the transistor will convey the L to the other side.
Note that current passes from the receiving side of the
channel to the transmitting side. The low output voltage of
the receiving side will be dependent upon the voltage at the
transmitting side plus the I • R drop of the pass transistor.
When a card socket is selected, it becomes a candidate to
drive data on the DATA pin and likewise receive data from
the DATA pin. When a card socket is deselected, the
voltage on its I/O A/I/O B pin will return to the idle state (H)
and the DATA side of that channel will become high
impedance. If both cards are deselected, the DATA pin will
be high impedance.
Both cards may be deselected at the same time to allow
communication with a second LTC1955.
Card channel A includes provision for unidirectional com-
munication with the C4 and C8 pins of the smart card. The
C4, C8 and I/O pins of card A are individually multiplexed
to the DATA pin using bits D11 and D12 as shown in
Table 4.
CCA
CCA/B
READY status, then $BE00 should be rewritten on
CCA
voltages at the I/O A/I/O B pins.
set to 3V, card selected, I/O A connected to
sn1955 1955fs