When a transaction sends data to a terminal, the EPI generates either a CICS_EPI_EVENT_SEND event or a CICS_EPI_EVENT_CONVERSE event.
The CICS_EPI_EVENT_SEND event indicates that data was sent but that no reply is required. Typically this would result from an EXEC CICS® SEND command, but in some servers it would result from an EXEC CICS CONVERSE command. (In the latter case, a CICS_EPI_EVENT_CONVERSE event occurs later to tell the application to send a data stream back to the transaction in the server.)
The CICS_EPI_EVENT_CONVERSE event indicates that a reply is required, and would typically result from an EXEC CICS RECEIVE or EXEC CICS CONVERSE command. The application must respond to this event by issuing a CICS_EpiReply call to provide the response data. The CICS_EpiReply function should be issued only to respond to a CICS_EPI_EVENT_CONVERSE event; if it is issued at any other time, an error is returned.