LTC1955 데이터 시트보기 (PDF) - Linear Technology

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LTC1955

Dual Smart Card Interface with Serial Control

Linear Technology 

LTC1955

Operation

Table 1. Serial Port Comand

STATUS OUTPUT

CARD B 0

0

0

0

Card B Electrical Fault

Card B ATR Fault

Card B VCC Ready

Card B Present

CARD A 0

0

0

0

Card A Electrical Fault

Card A ATR Fault

Card A VCC Ready

Card A Present

BIT COMMAND INPUT

D0 VCCB Options

D1 (See Table 2)

D2 Card B Select/Deselect

D3 Data Pull-Up Defeat

D4 Reserved (Always Set to “0”)

D5 Card B Clock Options

D6 (See Table 3)

D7

D8 VCCA Options

D9 (See Table 2)

D10 Card A Select/Deselect

D11 Card A Communications

D12 Options (See Table 4)

D13 Card A Clock Options

D14 (See Table 3)

D15

Table 2. VCC and Shutdown Options

D9 D8 STATUS (CARD A)

D1 D0 STATUS (CARD B)

0

0 VCC = 0V (Shutdown)

0

1 VCC = 1.8V

1

0 VCC = 3V

1

1 VCC = 5V

Table 3. Clock Options

D7 D6 D5 CLOCK MODE (CARD B)

D15 D14 D13 CLOCK MODE (CARD A)

0

0

0 Synchronous Mode

0

0

1 Unused

0

1

0 Asynchronous Stop Low

0

1

1 Asynchronous Stop High

1

0

0 Asynchronous ÷1

1

0

1 Asynchronous ÷2

1

1

0 Asynchronous ÷4

1

1

1 Asynchronous ÷8

To receive status data from the serial port, a read/write op-

eration must be performed. When polling for the presence

of a smart card on both channels, the input word should

be set to $0000 since this is the shutdown command 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 (VCCA set to

3V, card selected, I/O A connected to 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 VCCA ready

status, then $BE00 should be rewritten on 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 VCCA/B voltages at the I/O A/I/O B pins.

An NMOS pass transistor performs the level shifting. The

gate of the NMOS transistor is biased such that the transis-

tor is completely off when both sides have relinquished

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

communication 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.

10

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