the cpu 501 sends the rtp disable enable command in a command disabling condition step s 1103 subsequently it sends of the normal commands implemented in the printer 101 a status request command requesting the printer to return status information step s 1104 the cpu 501 waits for the status information to be returned by the printer 101 step s 1105 and after receiving the status information it sends the data stream of that normal command step s 1106 and finally sends the rtp disable enable command in an enabling condition step s 1107 this process is then terminated the reason why the status request command is sent in step s 1104 and the procedure then waits for the status information in step s 1105 is as follows there is a possibility of the occurrence of a time difference from when the printer 101 receives an rtp disable enable command until this command is executed and the rt flags in the printer 39 s flag memory are set correspondingly for example if an rtp disable enable command for disabling a particular real time command is sent and a data stream accidentally including the corresponding false real time command is sent immediately after the rtp disable enable command the command to be disabled may in fact be executed therefore the printer 101 has a function whereby its own status including the rt flags is stored in a memory as status information and is sent in response to a status request command from the host computer hence through the use of this function it is possible to verify whether the instructed setting of the rt flags is carried out or not as explained before when the printer 101 receives the rtp disable enable.