# Demand Polling

In TCP connection, when a periodic request is not received from the Host, the Display unit checks for the presence of a Host by performing Demand Polling.

When the Host receives this request, be sure to send a similar Demand Polling request to the Display. After the Display receives this request, it confirms the presence of the Host.

If no response is received from the Host, the Display will close the connection.

If you wish to use Digital Electronics Corporation APIs for the Host, the response processing of the Demand Polling request will be performed automatically by the API.