User`s guide

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If a nonzero Request ID is supplied, this function checks for the completion of only the function
associated with the ID.
If the return code is zero, the application should check the returned data string for information
pertaining to the completion of the requested asynchronous function.
The communications subsystem allows for a maximum of 20 asynchronous
requests per application to be outstanding. A return code for unavailable resources
(RC = 11) is returned if more than 20 asynchronous requests are attempted.
Note