Communication subsystem with an automatic abort transmission upon transmit underrun

Claim 1

In combination with a data processing system comprising a system bus, at least one central processing unit (CPU), one main memory, one peripheral controller, each individually coupled to said system bus, a communications subsystem also coupled to said system bus, said communications subsystem including a communications controller coupled to said system bus and also including typical communication devices such as a modem, a dialing unit and a touch-tone receiver coupled to said communications controller, said communications controller controlling the receipt and transmission of messages by said data processing system, said communications controller comprising: (a) a microprocessor coupled to main memory for receiving a data byte of information from said main memory; (b) a universal synchronous receiver transmitter (USRT) coupled to said microprocessor for receiving the data byte of information from said microprocessor, said USRT further generating an underrun signal and a series of flag byte signals when said microprocessor fails to transmit a data byte to said USRT within a predetermined time interval; and (c) first means responsive to said underrun signal for generating a predetermined signal and superimposing the predetermined signal on one of the series of flag byte signals thereby generating an abort sequence of a predetermined number of binary ONE bits.