Status responding device for supplying status information responsive to status transmission request

Even when a printer is in a condition incapable of receiving commands from a personal computer (PC), a status responding mode can be switched to ON in accordance with a request from the PC, thereby allowing detailed status information of the printer to be transmitted to the PC. When a printer is in an error condition when it is powered or reset, the printer rejects reception of data on a data line. Therefore, the mode of the printer cannot be changed with a set command transmitted from the PC to the printer through the data line. In view of the fact that the printer is capable of receiving signals on control lines even if the printer is in the error condition, the PC outputs a status transmission request through the select-in line for a predetermined number of times, so that a status transmission request interrupt process can be executed and then a parameter DEVICE is set to ON. Thereafter, the PC is capable of gathering detailed status information of the printer by merely transmitting the status transmission request to the printer.