Solution:

First of all, PC-ComLIB don't support PCL-844+. PCL-844+ use "PComm Pro" library. As you know the function 'sio_getports' of PC-ComLIB is used for "gets the number of ports and stores PORT NO. in a specified array. The PORT NO., which is set in the SETUP.EXE program, is an identification for each port". However, Pcomm Pro don't provide such function, and seems use 'sio_open(port no.)' to see if the specified port existed is the only way to solve this problem.