- Passive function propagation is utilized when signals enter and are passed through to an output of a part, such that visibility to each input signal remains. This method is useful for cases like multiplexers and buses, as well as passive components like resistors and capacitors.
The following diagram depicts three cases in which functions are propagated passively:
Passive propagation is used when a function depends upon one and only one input (or bidirectional) port.
In all three examples at left, the output is passive because the output function depends upon a single input.
For object Y, two signals enter the object at a single port and are passively propagated through the output.
Note: the control input to object Z does not count as an input when determining whether dependent output functions are active or passive.
In each case, the name of the output signals (net functions) reflect those of the original input signals.
In actual eXpress designs, net function names also reflect the object and port through which the function was passively propagated (for more details, refer to the discussion of Net Function Naming).
When to Use Passive Function Propagation
- Passive propagation is most often used for cases where it is preferable to retain visibility to the originating functions. As a general rule of thumb, the following types of devices are typically modeled passively:
