| 摘要 |
PROBLEM TO BE SOLVED: To provide a duplex communication circuit which quickly performs system switching to a LAP-B circuit for a preliminary system and also performs switching without interrupting LAP9-B protocol communication when a LAP-B circuit for the current operation system fails in a duplex communication system which has 1st and 2nd LAP-B circuits for one LAP-B communication line. SOLUTION: This circuit is provided with protocol controllers 73 and 83 which manages the control of a receiving function and a transmitting function and a LAP-B protocol, a communication management controller 40 having a register holding the preceding LAP-B protocol state and a transmission switching part 30 which selects a transmission signal to a transmission communication line 20 and transmission signals from two CCEs (protocol communication controller) 70 and 80 according to an instruction of the controller 40 inside the CCEs 70 and 80, and the controller part 40 parallelly operates the two CCEs 70 and 80, compares and monitors the states of the two CCEs 70 and 80 to detect a fault and has a function that selects a CCE accessing a receiving buffer and a function selecting a transmission signal to the line 20.
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