The Delay Transform delays the delivery of transitions for a specified time or a tick period. (Other Signal Processing Transforms read their input ports and transmit from their output ports in a single tick.)
A single Delay Transform can have multiple input and output ports. When a port is connected, a new port is added. Note that, by default, the input (right side) and output (left side) ports are reversed compared to other Transforms.
There are several cases where it is necessary to delay transitions until the next tick of the Harness (Z-1):
•From a control point of view you may just want to slow the progression of a transition. For example you may want to produce two Signals that are out of phase (like a quadrature output).
•More importantly, you may want to take an output Signal from a Transform and feed it back into your model at a point upstream. It is only possible to do this if you use the value of the Signal from the last tick cycle. A simple example is when you feed back the output of an Or gate to one of its input legs. This produces a latch. The feedback path has to include a Z-1 Delay Transform.
•In a closed-loop control system, you typically have two models. Outputs from each model are fed to inputs of the other. In this case, all signals that pass between the blocks need to pass through a Z-1 Delay Transform. The SIL Easy Cruise Control Sample Project demonstrates a closed-loop system using delays.
A Closed-Loop System with Delays from the SIL Easy Cruise Control Sample Project
Set the following properties:
•Delay Type – Select if incoming transitions are to be delayed by one tick or an amount time.
•Tick Delay – This should be set to 1.
•Time Delay – The amount of time, in seconds, to delay the incoming transitions.
When the Delay Type is set to Tick, an incoming transition is delayed until the next tick before it is transmitted on an outport. However, the time stamp of the transition is not changed, so it appears in a TestCase as if it was not delayed. In the TestCase below, the transitions at 1, 2, and 3 seconds appear on both Signals at the time they were transmitted. The transition at 4 seconds does not appear on the Delayed Signal, because it was the last transition, and there was no next tick when it could be transmitted.