Abstract: Higher functions terminals and lower function terminals, as well as dual mode terminals that are selectively operated at either functional level, are simultaneously supported on a common control unit interface in an information handling system. Communications with single mode terminals are directed to a buffer portion having a predetermined base address. Each dual mode terminal contains a buffer that is partitioned into respective portions used for communications at different function levels. Communications at a lower functional level are conducted through the buffer portion containing the base address while communications at a higher functional level are redirected to a buffer portion containing shifted addresses. The control unit includes means for determining the suitable level of terminal function and adjusting the addressing of the terminal buffer accordingly.