Communications adapter for processing ATM and ISDN data

A communications adapter card provides an interface for a TI or E1 transmission line and a signal processing circuit which can be programmed to process receive and transmit data in either an ISDN or an ATM format. Preferably, two such interfaces and two such signal processing circuits are provided on the card, so that a single adapter card can be used for attachment to both an ISDN network and to an ATM network. Each signal processing circuit includes a pair of DSPs, each of which has a two port buffer extending to a parallel bus. All such DSPs are connected to a data bus. The DSPs in each signal processing circuit execute programs to operate in either an ATM mode or an ISDN mode.