User`s guide

Signal Concepts
3-9
moment inbetween because Simulink implicitly auto-promotes the rate of the
slower signal to match the rate of the faster signal before the addition
operation is performed.
In general, for
Variable-step and Fixed-step SingleTasking modes, when you
measure the value of a discrete signal between sample times, you are observing
the value of the signal at the previous sample time.
Sample Time Offsets. Simulink offers the ability to shift a signal’s sample times
by an arbitrary value, which is equivalent to shifting the signal’s phase by a
fractional sample period. However, sample-time offsets are rarely used in DSP
systems, and blocks from the DSP Blockset do not support them.
Continuous-Time Signals
Most signals in a DSP model are discrete-time signals, and all of the blocks in
the DSP Blockset accept discrete-time inputs. However, many blocks can also
operate on continuous-time signals, whose values vary continuously with time.
Similarly, most blocks generate discrete-time signals, but some also generate
continuous-time signals.
The sampling behavior of a particular block (continuous or discrete)
determines which other blocks you can connect as an input or output. The
following sections describe the behavior for two types of blocks:
•“Source Blocks”
•“Nonsource Blocks”
See Chapter 5, “DSP Block Reference,” for information about the particular
sample characteristics of each block in the blockset.
Source Blocks
Source blocks are those blocks that generate or import signals in a model. Most
source blocks appear in the DSP Sources library. See section “Importing
Signals” on page 3-62 to fully explore the features of these blocks.
Continuous-Time Source Blocks. The sample period for continuous-time source
blocks is set internally to zero, which indicates a continuous-time signal.
Simulink’s Signal Generator block is an example of a continuous-time source
block. Continuous-time signals are rendered in black when
Sample time
colors
is selected from the Format menu. When connecting such blocks to