JPS6479985A - Disk device - Google Patents

Abstract

PURPOSE:To drive the title device with a simple electronic circuit and to prevent an image from being disturbed by providing a plural number of flag members for detecting a rotational phase in prescribed positions within an area of a central angle <180 deg. against the rotational center of a recording medium. CONSTITUTION:A PG yoke 103 at a center hub 102 and a PG yoke 104 in a position at the central angle 90 deg. are provided. When this disk is used to a reproducing device for exclusive use of the existing format, a PG detecting pulse is generated twice each time the disk rotates, and a discrepancy of the interval in length is generated so that abnormality is detected not to work a spindle servo, thus resulting in an impossibility of driving the device. Consequently, it is prevented that a disk recorded in a new format is reproduced by mistake in the existing system to output a disturbed image. On the other hand, in a system for both new and existing formats, by adding a simple circuit using a one shot multivibrator, one of the PG detecting pulses generated twice per rotation can be neglected to enable a disk for the new format only to be reproduced as well, and also the discrimination can be facilitated as to which format is applied.