Browse Prior Art Database

Multiple Frequency Clocking System

IP.com Disclosure Number: IPCOM000082503D
Original Publication Date: 1974-Dec-01
Included in the Prior Art Database: 2005-Feb-28
Document File: 3 page(s) / 92K

Publishing Venue

IBM

Related People

Duke, KA: AUTHOR

Abstract

It frequently occurs that a unit of a computing system, designed to operate at a particular clock frequency, needs to communicate with a second unit designed to Operate at a different clock frequency. In particular, this occurs where one unit is designed to operate in two different systems which use different clock frequencies.

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Multiple Frequency Clocking System

It frequently occurs that a unit of a computing system, designed to operate at a particular clock frequency, needs to communicate with a second unit designed to Operate at a different clock frequency. In particular, this occurs where one unit is designed to operate in two different systems which use different clock frequencies.

A problem arises in such units when it is required to switch control of some part of the unit from one clock frequency to the other. If the clock oscillators are independent of each other, that switchover cannot be effected cleanly especially if the change is required to be made within a few cycles. The clock oscillators must therefore be locked together, even though their frequencies are different. The following illustrates how the switchover may be effected quickly and cleanly.

Fig. 1 illustrates two related clock pulse trains in which for each 5 cycles of A, B goes through 8 cycles. The two clocks are locked so that they maintain the same phase relationship in each major cycle period. That relationship may be maintained by altering the frequency of one train to maintain an equal overlap between pulses A1 and B1, as between pulses A3 and B5. Both clock trains run continuously and drive shift register commutators so that individual pulses within the major cycle may be identified. (Fig. 2).

When it is required to transfer control from one clock train to the other, the initial clock train is degated between pulses from the using system and the alternate clock t...