H8SLASH3028F datasheet(552/923 Pages) RENESAS

552 / 923 page

Rev. 2.00, 09/03, page 522 of 890

14.3.3

Data Format

Figure 14.3 shows the smart card interface data format. In reception in this mode, a parity check is

carried out on each frame, and if an error is detected an error signal is sent back to the transmitting

device to request retransmission of the data. In transmission, the error signal is sampled and the

same data is retransmitted if the error signal is low.

No parity error

Output from transmitting device

Parity error

Output from transmitting device

Output from

receiving

device

Legend

Ds:

Start bit

D0 to D7: Data bits

Dp:

Parity bit

DE:

Error signal

Figure 14.3 Smart Card Interface Data Format

The operating sequence is as follows.

1. When the data line is not in use it is in the high-impedance state, and is fixed high with a pull-

up resistor.

2. The transmitting device starts transfer of one frame of data. The data frame starts with a start

bit (Ds, low-level), followed by 8 data bits (D0 to D7) and a parity bit (Dp).

3. With the smart card interface, the data line then returns to the high-impedance state. The data

line is pulled high with a pull-up resistor.

4. The receiving device carries out a parity check. If there is no parity error and the data is

received normally, the receiving device waits for reception of the next data. If a parity error

occurs, however, the receiving device outputs an error signal (DE, low-level) to request

retransmission of the data. After outputting the error signal for the prescribed length of time,

the receiving device places the signal line in the high-impedance state again. The signal line is

pulled high again by a pull-up resistor.

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