| 摘要 |
A last number redial device which provides a valid dialing sequence/access code test, before the contents of a last number redial register are disturbed, is described. A first and a second register are alternately loaded with a first, threshold portion (N) of a telephone number (N+M) during a dialing sequence. The number of digits entered are counted. If the count is greater than a threshold amount (N+1), a toggle signal is produced indicating a valid number has been entered. A second, terminal portion of the telephone number produced during the dialing sequence is thereafter loaded to a third register. In this way, the entire number is loaded in the selected first or second register and the third register. If a last number redial sequence is initiated, the selected one of the first or second registers and the third register provide an output to the telephone line of the last dialed number. If a next dialing sequence is initiated, the other of the first or second registers is initially loaded with the threshold portion of the telephone number. If an invalid number or access code is detected, the contents of the registers storing the last number dialed are saved. If a valid number is detected, the terminal portion of the presently dialed number is stored in the third register and the presently selected one of the first and second registers and the third register become the last number redial register.
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