The sticky bit would be that the 3000's terminal I/O is essentially one-way-at-a-time: if the terminal device doesn't have a read request posted, then most data sent from the attached device will be discarded (the exceptions being break and subsystem break indications). And trying to do anything else with the terminal device will involve aborting the read request, doing the something else, and starting a new read request. If the OPTO22 protocol can work around this, you're probably OK. Otherwise, you will probably need to build a front-end processor of some sort. If you have questions, feel free to ask, but my COBOL is rustier than my SPL, and so I will probably present terminal I/O examples in the latter with heavy [ab]use of MPE intrinsics.