Apparatus and method of data transfer between systems using different clocks

Apparatus comprising:

• a first register containing a first data string;
• a first counter;
• means for detecting a selected state of said first counter to load the data contained in said first register into said counter in accordance with said detected state of said counter;
• means response to output signals from said first counter for selectively providing an enable signal in accordance with the state of said first counter;
• a second register containing a second data string;
• a second counter;
• means for detecting a selected state of said second counter to load the data contained in said register into said counter in accordance with said detected state of said second counter;
• means, responsive to outputs signals from said second counter, for selectively providing a second enable signal in accordance with the state of said second counter;
• and
• a recirculating state device fed by said enable signals to selectively permit or inhibit transfer of data fed to said recirculating state device in accordance with the state of said enable signals.

Apparatus, comprising:

• a first down counter;
• a first register containing data representative of a maximum value count of said counter;
• means for detecting a selected state of said first counter to load the data contained in said first register into said first counter to restart said counter at a said maximum value count;
• means responsive to states of said first counter for providing an enable signal from a list of states corresponding to valid states for said counter for which a transfer of data fed to said apparatus can occur;
• a second down counter;
• a second register containing data representative of a second maximum value count of said second counter;
• means for detecting a selected state of said second counter to load the data contained in said second register into said second counter to restart said counter at a said second maximum value count;
• means, responsive to states of said second counter, for providing a second enable signal from a second list of states corresponding to valid states for said second counter for which a transfer of data fed to said apparatus can occur;
• means for providing a recirculating state device responsive to said first and second selected enable signals, a pair of clock signals, and data associated with a first one of said pair of clock signals for outputting said data in association with a second one of said pair of clock signals when said enable signals are in a state indicating that a transfer of said data can occur.