Slide 25 of 65
The structure of signal assignment statement allows some flexibility. However, the signal type of the result on the right hand side must match the type of the signal being assigned. This is illustrated in the first two signal assignment statements.
The third assignment shows the use of a single after clause used to control how much simulation time must pass before the assigned signal takes on its new value.
As seen in the fourth example, multiple assignments can be made in a single statements by separating them with commas. This sequence of assignments is called a "waveform".
If a signal assignment statement has no after clause, a clause equivalent to "after 1 delta cycle" is implied. Delta cycles are key to the VHDL timing model and have been previously discussed in the VHDL Basics module.