Help wanted - accessing a serial port from 4gl

We need to be able to have a 4gl program talk directly to a specific serial port on an HP9000. We need to be able to send messages to this port and receive data back from the device attached to it. The program will be run by many users concurrently so we need to be able to buffer the data and detect which user incoming data is meant for. Presumably we could commission a C subroutine, but does any one know of any other way to do this. Are there any software packages or shareware that would do this job ? Thanks in advance, Richard Moon