Synchronizing signal switching system for synchronizing external storage devices

Claim 2

A synchronizing signal switching system for synchronizing operations of a plurality of disk devices connected to a host controller in accordance with a master synchronizing signal generated by one of said disk devices as a master disk device, each of said disk devices comprising: a disk unit, included in each of said disk devices; and synchronizing signal switching means (100), included in each of said disk devices and opera­tively connected to said disk unit, for generating a synchronizing signal to be supplied to said disk unit, one of said disk devices being a current master disk device for currently supplying said synchronizing signal as a master synchronizing signal and another one of said disk devices being a next master disk device; said disk devices being connected in a sequence with a predetermined order to form a loop (16) through which said master synchronizing signal is transmitted; said synchronizing signal switching means in each of said disk devices being provided with an inheritance order to become said current master disk device and said next master disk device; wherein when said current master synchro­nizing signal is deteriorated, the synchronizing signal switching means having the next inheritance order is switched to supply the synchronizing signal as the current master synchronizing signal to all of said disk devices through said loop.

Claim 3

A synchronizing signal switching system as claimed in claim 1, wherein said synchronizing signal switching means in each of said disk devices comprises: synchronizing signal generating means (18) for generating said synchronizing signal including a synchronizing index signal and disk identifying information for identifying the disk device generating said synchronizing signal; inheritance priority judging means (20), operatively connected to said synchronizing signal generating means, for judging whether the disk device in question is said current master disk device or is said next master disk device for outputting said master synchronizing signal, by comparing said disk identifying information in the received master synchronizing signal with the disk identifying information in the generated synchronizing signal; deterioration detecting means (22) for detecting whether there is trouble in said master synchronizing signal received through said loop; and switching means (24), operatively connected to said synchronizing signal generating means, to said inheritance priority judging means and to said deterioration detecting means, for switching the output of the disk device from said master synchronizing signal received from the current master disk device through said loop into said synchronizing signal generated in the disk device in question, when said deterioration detecting means detects trouble in said master synchro­nizing signal received through said loop and when said inheritance priority judging means judges that the disk device in question is the next disk device for output­ting the master synchronizing signal.

Claim 4

A synchronizing signal switching system as claimed in claim 1, wherein said plurality of disk devices (10-1 to 10-n) each having a master pulse input terminal (12) and a master pulse output terminal (14), the disk devices being sequentially connected in a predetermined order into said loop by connecting the master pulse output terminal (14) of each of the disk devices to the master pulse input terminal (12) of the next one of the disk devices through a transmission line (16).

Claim 5

A synchronizing signal switching system as claimed in claim 2, wherein said switching means (24) comprises switch control means (26), operatively con­nected to the outputs of said synchronizing signal generating means, of said inheritance priority judging means, and of said stoppage detecting circuit, for providing said master synchronizing signal in response to the outputs of said synchronizing signal generating means, of said inheritance priority judging means, and of said stoppage detecting circuit.

Claim 6

A synchronizing signal switching system as claimed in claim 4, wherein said switch control means (24) comprises master synchronizing signal providing means, said master synchronizing signal being the synchronizing signal generated by its own synchronizing signal generating means under the condition when said inheritance priority judging means judges that the disk device in question is the current master disk device and when said deterioration detecting means does not detect the deterioration of said master synchronizing signal received from the other disk device through said loop, and said master synchronizing signal being the synchro­nizing signal received from the other disk devices through said loop under the condition when said inheritance priority judging means judges that the disk device in question is the next master disk device and when said deterioration detecting means does not detect the deterioration of said master synchronizing signal received from the other disk device through said loop.

Claim 7

A synchronizing signal switching system as claimed in claim 4, wherein said switch control means (24) comprises master synchronizing signal providing means, said master synchronizing signal being the synchronizing signal received from other disk devices through said loop under the condition when said inheri­tance priority judging means judges that the disk device in question is the next master disk device and when said deterioration detecting means does not detect the deterioration of said master synchronizing signal received from the other disk device through said loop, and said master synchronizing signal being the synchro­nizing signal generated by its own synchronizing signal generating means under the condition when said inheri­tance priority judging means judges that the disk device in question is the next master disk device and when said deterioration detecting means detects the deterioration of said master synchronizing signal received from the other disk device through said loop.

Claim 8

A synchronizing signal switching system as claimed in claim 4, wherein said switch control means (24) comprises master synchronizing signal providing means, said master synchronizing signal always being the synchronizing signal received from other disk devices through said loop irrespective of the output of said deterioration detecting means, under the condition when said inheritance priority judging means judges that the disk device in question is neither the current master disk device nor the next master disk device.

Claim 9

A synchronizing signal switching system as claimed in claim 2, wherein said deterioration detecting means comprises index pulse latching means for continu­ously latching a plurality of said index pulses, whereby when at least one of said index pulses is not latched, said deterioration detecting means detects a deteriora­tion in the received master synchronizing signal.