| 摘要 |
<p>It is known when testing digital lines in a telecommunication system to send a data word from a test point at an exchange, for instance, to a remote point such as a subscriber's equipment. There it is echoed back to the exchange, either unmodified or modified in a predetermined manner, and the echoed back version compared with the original. The result of the comparison indicates whether the line - or the subscriber's equipment - is corrupting the data. This is extended, in the present arrangement, by reading the test word form a ROM from which it is sent to the subscriber's equipment, which echoes it back, either unmodified or modified in a predetermined manner, to the exchange. There the echoed back version is used as the address for the ROM and this gives an effective comparison, which is completed by an EXCLUSIVE OR gate connected between the input and output least significant bits of the ROM.</p> |
