System management mode circuits, systems and methods

A personal computer comprising:

• an input device;
• a memory;
• a display;
• a microprocessor chip coupled to said input device, said memory, and said display;
• and
• an integrated circuit comprising:
• a data source supplying data and successive valid data control signals, wherein transitions occur in the data during intervals between said valid data control signals;
• a source of at least one quieting control signal independent of said valid data control signals;
• a selector having a first input coupled to said data source, and a second input, and an output;
• a circuit coupled to said output of said selector to receive data from said data source via said selector;
• and
• a source of a quieting signal coupled to said second input, and said selector responsive to said at least one quieting control signal to select said quieting signal during at least a portion of the interval between said valid data control signals, and to select said data source in response to at least some of said valid data control signals;
• and
• a bus coupling said microprocessor chip and said integrated circuit said bus coupled to said output of said selector.