Method for operating a register stage of a dual function data register
A method for operating a register stage of a dual function data register. A data register having master and slave latching circuits is used for concurrently storing two different words of data. Data is shifted into the master latching circuit in response to a first clock signal, and data stored in the master latching circuit is shifted into the slave latching circuit in response to a second clock signal. The first and second clocks are generated from a source clock in response to a control signal, which can be asserted at different times to initiate shifting operations from either the master latching circuit or the slave latching circuit. In otherwords, shifting operations can be initiated either on a rising edge of the source clock, or on a falling edge of the source clock.
1. A method for operating a register stage having a first latch and a second latch arranged in a master-slave flip-flop configuration for storing a first bit of data and a second bit of data respectively, comprising:
a) decoupling the first latch from a serial input terminal and decoupling the second latch from the first latch at the same time while a source clock signal oscillates; and,
b) initiating a shifting operation on either a high logic level of the source clock or a low logic level of the source clock for shifting one of the first bit of data and the second bit of data.
2. The method of claim 1 , wherein the step of decoupling includes turning off a first gating device between the first latch and a serial input terminal and turning off a second gating device between the first latch and the second latch.
3. The method of claim 2 , wherein turning off includes driving a first clock signal to an inactive logic level for turning off the first gating device, and driving a second clock signal to the inactive logic level for turning off the second gating device.
4. The method of claim 3 , wherein the first clock signal and the second clock signal are driven to the inactive logic level by maintaining a shift enable signal at the inactive logic level while the source clock signal oscillates.
5. The method of claim 2 , wherein the step of initiating includes turning on the first gating device while the second gating device is turned off for shifting the second bit of data.
6. The method of claim 5 , wherein turning on the first gating device includes driving a first clock signal to an active logic level.
7. The method of claim 6 , wherein the first clock signal is driven to the active logic level when a shift enable signal is enabled while the source clock signal is at a first logic level, the second clock signal being driven to an inactive logic level when the shift enable signal is enabled while an inverted source clock signal is at a second logic level.
8. The method of claim 7 , wherein the step of initiating includes turning on the second gating device while the first gating device is turned off for shifting the first bit of data.
9. The method of claim 8 , wherein turning on the second gating device includes driving the second clock signal to the active logic level.
10. The method of claim 9 , wherein the second clock signal is driven to the active logic level when the shift enable signal is enabled while the source clock signal is at the second logic level, the first clock signal being driven to the inactive logic level when the shift enable signal is enabled while an inverted source clock signal is at the first logic level.