ComOpen

This function must be called by an application before it can use a communications port. The call opens a communication port, pre-allocates and initializes the System Manager resources needed; clears the transmit and receive buffers; and, if successful, returns a "handle" to the application to use for all subsequent port activity.

There is the possibility that ComOpen could fail due to a lack of System Manager resources is one cause, so the application should be able to handle this condition.


Syntax:          err_t far ComOpen(handle_t far *Handlep, int PortId) 
Parameters:      handle_t far *Handlep - Far pointer to a handle_t variable which will
                                         receive a "handle" to the communication port
                                         which must be provided on all subsequent com 
                                         driver functions 
                 int PortId - Identifier specifying the communication port to open 

                              COM_LINE_1 (COM1) and COM_LINE_2 (COM2) for the HP 
                              palmtop
                              COM_LINE_4 (COM4) for the connectivity pack 
Returns:         0 - for success 

                 E_IVCHN - if communication port number requested is out of range, 
                           or if port is not configured 
                 ComOpen may also fail because of System Manager resource shortages 
                 (ERESOURCE), or because a port (an alternate) was not properly defined
                 (no hardware addresses or IRQ: EBADPORT), or because an illegal 
                 parameter was supplied (EINVALID).  
Related Calls:   The ComAcquire call must be made to acquire use of the port after it 
                 is opened.