Multiple-speed interface

A method for processing an audio/video signal using a security module comprising a processor configured to process the audio/video signal, an interface comprising a plurality of contacts including a power supply contact and a clock contact configured to receive a clock signal, a frequency divider configured to divide a frequency of the clock signal to generate a divided clock signal, a frequency multiplier configured to multiply the frequency of the clock signal to generate a multiplied clock signal, or both, a voltage detector configured to measure a voltage on the power supply contact, and a multiplexer configured to select between the received clock signal or divided clock signal or multiplied clock signal for operating the security module, said method comprising:

• powering the security module via the power supply contact;
• measuring a voltage on the power supply contact;
• determining a category to which the measured voltage pertains, said category being one from a plurality of predetermined categories;
• selecting an operation mode from a plurality of predetermined operation modes, said selection depending on the determined category, each of the predetermined operation modes having a frequency of operation corresponding to a frequency of one of the received clock signal, divided clock signal, or multiplied clock signal, the predetermined operation modes including any communication protocol from a plurality of different communication protocols or any class from a plurality of classes of a communication protocol;
• selecting between the received clock signal or divided clock signal or multiplied clock signal with the multiplexer corresponding to the selected operation mode;
• and
• operating the security module according to the selected operation mode.

A system for decoding an audio/video data stream, said system comprising:

• a decoder comprising:
• a security module interface configured to interface with a security module, said security module interface comprising a least a power terminal configured to supply power to the security module and a clock terminal configured to supply a clock to the security module;
• a clock generator configured to generate a first clock having a first clock frequency and connected to supply the first clock to the clock terminal;
• and
• a power supply connected to supply power to the power terminal;
• wherein the decoder is configured to set a voltage supplied to the power terminal to correspond to one from a plurality of predetermined voltage ranges, each of the predetermined voltage ranges corresponding to a communication protocol from a plurality of different communication protocols or a class from a plurality of classes of a communication protocols;
• and
• the security module comprising:
• a processor configured to process the audio/video data stream;
• an interface comprising a plurality of contacts including a power supply contact configured to interface with the power terminal of the security module interface and a clock contact configured to interface with the clock terminal of the security module interface and receive the first clock;
• a frequency divider configured to divide a frequency of the first clock to generate a divided clock signal, a frequency multiplier configured to multiply the frequency of the first clock to generate a multiplied clock signal, or both;
• a voltage detector configured to measure a voltage on the power supply contact and to categorize the measured voltage as pertaining to one from the plurality of predetermined voltage ranges;
• and
• a multiplexer configured to select between the first clock or divided clock signal or multiplied clock signal for operating the security module;
• wherein said security module is configured to function according to any one from a plurality of predetermined operation modes, each of the predetermined operation modes having a frequency of operation corresponding to a frequency of one of the received clock signal, divided clock signal, or multiplied clock signal, the predetermined operation modes including any communication protocol from a plurality of different communication protocols or any class from a plurality of classes of a communication protocol;
• and
• wherein the security module is configured to monitor for a change in a category of the measured voltage from the voltage detector following power-on and, when the security module detects the change in the category, to switch to a different one from the plurality of operating modes and to cause the multiplexer to select between the first clock or divided clock signal or multiplied clock signal corresponding to the different one from the plurality of operation modes.