To provide a computer program for attaining a function of a communication system capable of autonomously starting a specific communication event by a user's operation on a peripheral device side in spite of the fact that the issuing direction of commands conducting execution of communication events is regulated to one direction from a PC side to the peripheral device side.

The peripheral device generates a peripheral device-side trigger for urging a host device to start a target communication event based on the user's operation, and the host device issues a trigger report request command for monitoring generation of the peripheral device-side trigger in the peripheral device toward the peripheral device according to a main communication protocol. The host device receives trigger generation report information from the peripheral device which has received the command, and starts the target communication event when presence of the peripheral device-side trigger is determined from the content of the trigger generation report information.

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