| 摘要 |
PURPOSE:To improve the operability by providing an endless belt turned by channel selection operation, an unlock command generating means responding to the operation, a turning direction detection means and a means generating a pulse in response to the turning of belt. CONSTITUTION:The endless belt 25 is provided with pulse marks comprising single phase mark and biphase mark in combination. The pulse marks are detected by mark sensors 26a, 26b and inputted to a phase detector 28. When the detection order of both the marks is, e.g., in the forward direction, the level of a terminal 28a goes to an L level and to switch 29 is operated. Thus, a moving contact 29a and a normally closed contact 29a are kept closed to send a down-pulse to a terminal D of an up-down counter 8. An unlock command is generated by an unlock switch 30 closed in depressing the belt 25. The command is sent to a terminal E of the counter 8 via a channel selection control circuit 6.
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