The System Manager's Communication services provide access to the HP palmtop's serial port.
Applications using the Communication services must include COMIO.H and INTERFAC.H.
Note that all Communication driver calls are "non-blocking," that is, if the operation cannot be completed in a short enough time interval (actual time depends upon the operation), the operation is declared complete, with partial results returned. This typically only affects operations such as read or write where large delays may be experienced.
For example, an application can try to read 1000 characters, but if 1000 characters are not currently available, then the read will return with fewer characters than requested. This, however, is not an error. Similarly, if an application tries to write 10,000 characters, the Communication driver will copy as many characters as possible into internal buffers, and notify the caller of the number of characters actually accepted. It is up to the caller to repeat the request until the operation is completed.