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LTC1955 Datasheet(PDF) 9 Page - Linear Technology |
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LTC1955 Datasheet(HTML) 9 Page - Linear Technology |
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9 / 22 page  LTC1955 9 1955fd For more information www.linear.com/LTC1955 operaTion Serial Port The microcontroller compatible serial port provides all of the command and control inputs for the LTC1955, as well as the status of the two smart cards. Data on the DIN input is loaded on the rising edge of SCLK. D15 is loaded first and D0 last. At the same time, the command bits are being shifted into the DIN input, the status bits are being shiftedoutoftheDOUToutput.Thestatusbitsarepresented to DOUT on the rising edge of SCLK. Once all bits have been clocked into the shift register, the command data is loaded into the command latch by bringing LD low. At this time, the command latch is updated and the LTC1955 will begin to act on the new command set. The status data is latched into the shift register on the rising edge of LD. SCLK should be low when LD is brought low and should be high when LD is brought high. This requires a 9th clock cycle per transaction. Figure 1 shows the recommended operation of the serial port. Multiple LTC1955s may be daisychained together by connecting the DOUT pin of one LTC1955 to the DIN pin of another. Figure 6 shows an example of multiple LTC1955s daisychained together. The maximum clock rate for the serial port is 10MHz. The serial port controls the following parameters of each smart card socket: • Selection/deselection of a smart card • VCC voltage level of each card (5V/3V/1.8V/0V) • Clock mode of each card (synchronous or asynchronous) • Operating mode of asynchronous cards (clock stop high, low, ÷1, ÷2, ÷4 or ÷8) • Selection of the I/O, C4 or C8 pins for card socket A The serial port provides the following status data: • It indicates the presence or absence of the smart cards. • ItindicatesthereadinessofthesmartcardVCCsupplies. Communication with a smart card is disabled until its power supply voltage has reached the final value. • It indicates fault status. In the event of an electrical or ATR fault, the fault is reported. For electrical faults, the LTC1955 will automatically deactivate the smart card. Table 1 illustrates the command inputs and status outputs associated with each bit of the serial data word. Three voltage options are available from the LTC1955: 5V, 3V and 1.8V. Bits D0, D1 (card B) and D8, D9 (card A) determine which voltage is selected. Setting both control bits of a channel to 0 deactivates that channel and sets the smart card supply voltage to 0V. If both channels are deactivated, the LTC1955 is in shutdown. Table 2 shows the operation of the supply control bits. The CLK A/CLK B pins to the smart cards can be pro- grammedforvariousmodes.Bothsynchronousandasyn- chronous cards are supported. There are several options available with asynchronous cards. Table 3 shows how all clock options are obtained using bits D5–D7 (card B) and D13–D15 (card A). The default state of the LTC1955 on power up is synchronous mode. DIN SCLK LD X D0 D15 X D1 DOUT D15 FROM INPUT D0 D15 1955 F01 D14 D5 D15 D1 tLC tDH tDD tDS tH tL tCL tLFC tCL READ/WRITE CYCLE D14 D2 Figure 1. Serial Port Timing Diagram |
Similar Part No. - LTC1955_15 |
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Similar Description - LTC1955_15 |
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