Remove data from output buffer
After the output buffer is flushed, the BytesToOutput property is automatically configured to 0.
If flushoutput is called during an asynchronous (nonblocking) write operation, the data currently stored in the output buffer is flushed and the write operation is aborted. Additionally, the callback function specified for the OutputEmptyFcn property is executed. You can write data asynchronously to the instrument using the fprintf or fwrite functions.
The output buffer is automatically flushed when you connect an object to the instrument with the fopen function.