1. Field of the Invention
This invention relates to an image forming apparatus comprising an image forming device, such as a laser printer for receiving image data from an external device and forming images on paper sheets in accordance with the image data, and various optional units connected to the image forming device.
2. Description of the Related Art
An image forming apparatus, such as a laser printer, which receives image data from an external device and forms image on paper sheets in accordance withe image data has already been put to practical use.
In most cases, optional devices, such as a paper feeder, a paper discharging device, a paper-reversing device and an auxiliary paper feeder, are connected to the laser printer, constituting an image forming system. Whether or not any of these optional devices is connected to the laser printer, the paper-reversing device and the auxiliary paper feeder are required to print an image on the reverse side of a paper sheet. Whether any optional device is connected to the laser printer is determined in accordance with whether or not data is transferred between the printer and the optional device. Hence, once the optional device is turned off, it is no longer possible for a user to see whether the optional device is connected or not connected to the laser. This is a problem inherent in the conventional image forming system.