Image forming device

An image forming device to form an image on a sheet of paper, comprising:

• a main body, and
• a submodule detachably disposed on the main body,
• the main body including an asynchronous serial bus,
• and a master control unit that is connected to the asynchronous serial bus, transmits a first signal onto the asynchronous serial bus, and detects, on the asynchronous serial bus, a second signal transmitted in response to the first signal at a scheduled timing,
• the submodule including a slave control unit that is connected to the asynchronous serial bus, and, when detecting the first signal transmitted from the master control unit on the asynchronous serial bus, transmits a second signal detectable by the master control unit in response to the first signal at the scheduled timing, wherein
• an interactive asynchronous serial communication is performed between the master control unit and the slave control unit,
• the master control unit includes a detection timing changing unit that changes the scheduled timing to detect the second signal from a first timing to a second timing in accordance with a predetermined rule, and
• a timing update notification transmission unit that transmits a notification signal to notify an update of the scheduled timing changed by the detection timing changing unit to the slave control unit onto the synchronous serial bus, and
• the slave control unit includes a timing update notification detection unit that detects the notification signal transmitted from the timing update notification transmission unit on the synchronous serial bus, and
• a transmission signal changing unit that changes a state of the second signal from a first state detectable by the master control unit at the first timing to a second state detectable by the master control unit at the second timing when the timing update notification detection unit detects the notification signal.