I/O control apparatus, POS system and printing apparatus including the I/O control apparatus, and a data relay processing method for the I/O control apparatus

Disclosed is an I/O control apparatus (12) that enables a POS system to add new functions to the existing system without changing the existing POS system program. At least one of connection ports (21b to 23b) of the I/O control apparatus (12) is connected to at least one the connection ports (21a to 23a) of an existing POS terminal (30) having at least a POS printer (34), a input device (32), or a display (33) connected thereto. The input devices (32 to 34) conventionally connected to the ports (21 a to 23a) of the POS terminal (30) are connected to the corresponding ports of the I/O control apparatus (12). A function-adding server (50) is also connected to the I/O control apparatus (12). When relaying data communication between the input devices (32 to 34) and the POS terminal (30), the I/O control apparatus (12) monitors the received data. If information meeting specific identification criteria is detected in the received data, the I/O control apparatus (12) informs the function-adding server (50) and thus receives additional functionality from the server (50).