Interleaving a conversation with message routing

While you are building a message to be routed, you can use BMS SEND commands as well as RECEIVE MAP and terminal control commands to converse with your principal facility.

Such SEND commands must have a disposition option of TERMINAL rather than PAGING or SET, and must not specify ACCUM. The associated inputs and outputs are processed directly and do not interfere with your logical message, even if your terminal is one of the destinations of the message.

Without routing, you cannot use BMS SENDs, as noted in Building logical messages.