The minimum time required to obtain a valid output at an output pin that is fed by a register after a clock signal transition on an input pin that clocks the register. This time always represents an external pin-to-pin delay.
In the Quartus® Prime Standard Edition software, you can specify the required minimum tCO for the entire project and/or any clock signal, any register driving an output or bidirectional pin, or any output or bidirectional pin driven by a register. You can also specify a point-to-point minimum tCO requirement between a clock and a register, a clock and an output pin, or a register and an output pin.
minimum tCO is calculated using the following equation:
minimum tCO = <shortest clock to source register delay> + <micro clock to output delay> + <shortest register to pin delay>