| 摘要 |
An alphanumeric terminal providing a digital message having a fixed portion consisting of the address of the receiver in sixteen bits, followed by a repeat of the address in sixteen bits, a status indication in four bits, a request in four bits and an acknowledge plus an indication of whether text follows in two bits; and a variable portion consisting of a text message of zero to 384 bits, which fixed and variable portions of the message have parity bits inserted after each digital word and are delayed and interleaved (every other bit) with a similar undelayed message to form a composite message, which composite message is preceded by a pseudo random code of 127 bits. The terminal also includes noise and error detection circuitry, associated with the receiver, which separates the two interleaved messages and compares them for similarity, checks the parity bits for correctness and compares the amplitude of each bit to a predetermined upper and lower level to determine whether the bit is noise or a portion of the signal. From the various noise and error checks the terminal then provides a decision as to whether a digital word is good or bad and, if the digital word is in error and comes within the text portion of the message, an asterisk appears in the visual display so that the operator can mentally determine what the character should be. |
