Card system, IC card and card reader/writer used for the card system

摘要

A card system comprising an IC card and a card reader/writer wherein when data is transmitted and received over a signal line between said IC card and said card reader/writer for reading or writing of the data, a data transmitting side transmits a parity based upon content of the data together with the data over the signal line and a data receiving side checks whether or not there is any error in reception of data based upon content of the data and the parity received to transmit back to the data transmitting side a data retransmission request signal for requesting the data transmitting side to retransmit the data when there is an error; and wherein said IC card corrects a level of said signal line for requesting the data transmitting side to transmit next data when it is verified that there is no error in the reception of said data based upon content of said data and said parity received by the data receiving side.