The present invention relates to communication systems, communication devices, wired communication devices, and communication methods. More particularly, the invention relates to a communication system, a communication device, a wired communication device, and a communication method that can perform wired communication with a simple configuration of the devices by minimizing the number of lines for connecting the devices.
Integrated circuit (IC) cards that can perform near field communication, which is one type of wireless communication, are coming into widespread use because of its utility. Such IC cards that perform near field communication are used in, for example, an automatic ticketing system in a station or an electronic settlement system that conducts settlement by using e-money.
Due to the spread of near field communication IC cards, the standardization of near field communication protocols that can be used by IC cards is in progress. A typical example of such communication protocols is Near Field Communication Interface and Protocol (NFCIP)-1, which is defined as ISO/IEC 18092.
NFCIP-1 defines two communication modes, i.e., an active mode and a passive mode. In the active mode, to send data, a plurality of communication devices each output electromagnetic waves and modulate them by themselves. In the passive mode, to send data, one of a plurality of communication devices outputs electromagnetic waves and modulates them, and another communication device receives the electromagnetic waves and performs load modulation on them. Communication devices based on NFCIP-1 perform communication either in the active mode or the passive mode (see, for example, Japanese Unexamined Patent Application Publication No. 2004-215225 and “Information Technology Telecommunications and Information Exchange between Systems Near field Communication Interface and Protocol (NFCIP-1)”, First Edition 2004-04-01, ISO/IEC 18092:2004(E)).
In addition to IC cards, cellular telephones are now widely used, and a device integrating an IC card and a cellular telephone therein, i.e., a cellular telephone having a built-in IC card that performs near field communication, is already put to practical use. More precisely, a cellular telephone integrates an IC chip rather than an IC card therein, that is, the shapes of the IC card and the IC chip are different although the functions thereof are similar. For the convenience of description, however, IC chips having functions similar to those of IC cards are also referred to as “IC cards”.
Some cellular telephones are designed to allow users to install and remove subscriber identity module (SIM) cards (which include SIM chips) storing subscriber information (for example, telephone numbers) necessary for the users to use the cellular telephones. Such cellar telephones are hereinafter referred to as “SIM-compatible cellular telephones”.
If the user replaces a currently used SIM-compatible cellular telephone by another SIM-compatible cellular telephone, he/she can remove the SIM card from the old one to insert it into the new one to use the new cellular telephone.
As the standards superior to SIM, user identity module (UIM) is available. UIM cards (which include UIM chips) can handle, not only user subscriber information, but also personal information, such as credit card numbers and authentication information used for conducting authentication. SIM cards and UIM cards are defined in ISO7816.
SIM cards or UIM cards have terminals (pins) for performing wired communication with other devices to send and receive signals. When a SIM card or a UIM card is installed in a cellular telephone, the terminals of the SIM card or the UIM card are brought into contact with the terminals of the cellular telephone so that the circuit in the cellular telephone can send and receive signals to and from the SIM card or the UIM card by wired communication.
It is necessary that SIM cards or UIM cards be small since they are installed in portable machines, such as cellular telephones. Accordingly, only a small number of terminals, for example, about 8 terminals, are provided for sending and receiving signals to and from other devices, and some of the terminals are used for sending and receiving signals to and from the circuit in a cellular telephone.
As discussed above, currently, there are two types of cellular telephones, i.e., one type of which has a built-in IC card that performs near field communication, and the other type of which allows users to install and remove SIM cards or UIM cards (hereinafter simply referred to as “SIM cards”). It can be therefore expected that cellular telephones having built-in IC cards that perform near field communication and are compatible with SIM cards will be put to practical use and become popular.
In such cellular telephones, a communication interface used for performing near field communication by using an IC card is probably used for sending and receiving signals between a built-in SIM card and external devices.
In this case, it is necessary that such a near field communication interface be connected with the SIM card by physical lines (wires).
As stated above, however, only a small number of terminals are provided for the SIM card and some of them are already used. Accordingly, it is necessary to minimize the number of physical lines for connecting the near field communication interface with the SIM card.
On the other hand, if the number of lines is reduced, it is necessary that signals be sent and received with such a small number of lines, which increases the complexity of the communication interface and the SIM card.
More specifically, if signals are sent from the communication interface to the SIM card and also from the SIM card to the communication interface by using only one connecting line, it is necessary to change the impedance (impedance when viewed from an external source) in the communication interface or the SIM card between when a signal is sent and when a signal is received. Impedance changes further change voltages or currents, in which case, the detection of signals (for example, detecting the levels of received signals) should be performed by precisely considering such voltage or current changes. Additionally, when the SIM card is installed in a cellular telephone, the impedance when viewed from one of the communication interface and the SIM card to the other one may be changed depending on the condition of contact between the terminals of the cellular telephone and those of the SIM card. It is thus necessary to design the communication interface and the SIM card to cope with the above-described impedance changes or voltage or current changes. Thus, the configuration of the communication interface and the SIM card become complicated.
As the configuration of the communication interface or the SIM card becomes complicated, the size thereof is also increased. This is not preferable since the communication interface and the SIM card, in particular, the SIM card, should be small, as discussed above.