Patent ID: 7769091

Claim:
A communication system comprising: a first device; and a second device connected to the first device by a single communication line, wherein the first device includes a first transmitting portion which transmits to the second device a pulse signal set to a predetermined cycle that differs according to command data, and a first receiving portion which reads data transmitted from the second device based on a voltage value of a transmission signal transmitted over the communication line; and the second device includes a second transmitting portion which transmits to the first device a voltage signal set to a predetermined voltage value that differs according to the data, and a second receiving portion which reads the command data transmitted from the first device based on a pulse signal cycle of the transmission signal transmitted over the communication line, and an operating apparatus that operates based on the command data transmitted from the first device, wherein the first device further includes an abnormality detecting portion that detects an abnormality, and sets the command data transmitted to the second device to a pulse signal including a shortest cycle of a plurality of cycles when the abnormality is detected.