"Furthermore, once the data signal has been driven to the opposite value, the active circuit enters a passive state where it then becomes the passive circuit, whilst the previously passive circuit enters the low gain mode where it then becomes the active circuit monitoring the bidirectional communication path for the next transition in the data signal. As a result, the apparatus is self-configuring, thus avoiding the requirement for propagation of configuration signals as required by the prior art technique of FIG. 1. This hence provides further performance and energy consumption savings.
"In addition to the performance and energy consumption benefits that arise from the use of the apparatus of the present invention, the design is not dependent on the implementation details of the bidirectional communication path, and accordingly the design can be instantiated as a standard cell for use in a wide variety of different applications.
"The apparatus can be used for a variety of purposes within a bidirectional communication path. However, in one embodiment, the apparatus forms a repeater placed within the bidirectional communication path to amplify the data signal as that signal is propagated along the bidirectional communication path.
"In one such embodiment, the control circuitry in each of the first and second circuits receives as control input signals said signal from the transition detection circuitry indicating that said transition has been detected, and a signal indicative of the value of the data signal on the bidirectional communication path at an input to the first and second circuits, and is configured to control the transition of the associated first and second circuit between said passive state, said low gain state and said high gain state in dependence on those control input signals. Accordingly, the apparatus is self-configuring, and requires no externally provided configuration signal. Further, no clock signal is required for the apparatus, since both the first and second circuits transition between the low gain, high gain and passive states in dependence solely on the value of the data signal on the bidirectional communication path and the signal from the transition detection circuitry indicating that a transition has been detected, and hence the apparatus is entirely self-timed.
"Due to the self-timed nature of the apparatus, the apparatus can readily be used within a bidirectional communication path connecting two devices operating at different clock speeds.
"In one embodiment, if the value of the data signal at said input to the first and second circuits is a first value, the control circuitry of the first circuit is configured to place that first circuit in said low gain state where the first circuit is the active circuit, and the control circuitry of the second circuit is configured to place that second circuit in said passive state where the second circuit is the passive circuit. Conversely, if the value of the data signal at said input is a second value, the control circuitry of the second circuit is configured to place that second circuit in said low gain state where the second circuit is the active circuit, and the control circuitry of the first circuit is configured to place that first circuit in said passive state where the first circuit is the passive circuit.
"Furthermore, in one embodiment, when the transition detection circuitry of the active circuit detects said transition, the control circuitry of the active circuit is configured to cause that active circuit to change from the low gain state to the high gain state. However, the control circuitry of the passive circuit is configured to retain the passive circuit in the passive state until after the data signal has been driven to said opposite value by the operation of the active circuit in said high gain state. The repeater can be configured in a variety of ways. In one embodiment, the repeater acts as an inverter (with its two inputs having opposite values), whilst in an alternative embodiment the repeater acts as a buffer (with its two inputs having the same value).
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