| 摘要 |
PURPOSE:To make a circuit for loopback test needless and to simplify the constitution of a transmission device by comparing the test data returned from the transmission control unit of reception side with the test data at the time of having been transmitted in the transmission control unit of transmission side. CONSTITUTION:The transmission control unit 1 and the transmission control unit 2 of a data transmission system are connected through transmission lines l1 and l2 and the transmission-reception of each kind of data is executed between the units 1 and 2. Transmission parts 1-2 and 2-3 and reception parts 1-3 and 2-2 are controlled by the respective data input-output parts 1-1 and 2-1. And a code D1 which indicates a loopback and looped data D2 are transmitted repeatedly from the unit 1. The code D1 which indicates the loopback is decided in the unit 2 and the data D2 transmitted repeatedly is transmitted to the unit 1 as it is. In the input-output part 1-1 of the unit 1 which receives the data D2 the data D2 and the data D2 at the time of having been transmitted are compared and a loopback test is executed with only the looped data D2, so that the constitution of the system can be simplified.
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