The 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^® II software, you can specify the required t_CO 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 t_CO requirement between a clock and a register, a clock and an output pin, or a register and an output pin.

t_CO is calculated using the following equation:

t_CO = <clock to source register delay> + <micro clock to output delay> + <register to pin delay>