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Basic Elements 37
Xilinx Blocks
Block Parameters Dialog Box
The block parameters dialog box can be invoked by double-clicking the icon in your
Simulink model.
Figure 3-12: Down sample block parameters dialog box
Parameters specific to the block are:
• Sampling Rate: must be an integer greater or equal to 2. This is the ratio of the
output sample period to the input, and is essentially a sample rate divider. For
example, a ratio of 2 indicates a 2:1 division of the input sample rate. If a non-
integer ratio is desired, the Up Sample block can be used in combination with the
Down Sample block.
• Zero Initial Output (otherwise NaN): NaN means Not a Number. This
option lets you choose what the first value of the new sample (before it has valid
data) will be. By selecting Zero Initial Output, you can validate the first sample
with valid data of zero. Otherwise, an invalid data (NaN) will be the block’s first
output.
Other parameters used by this block are explained in the Common Parameters section
of the previous chapter.
The Down Sample block does not use a Xilinx LogiCORE.
Get Valid Bit
The Xilinx Get Valid Bit element sets its output to 1 when its input is a
valid data value. The output is set to 0 otherwise.
In the Xilinx Blockset, every data sample that flows through the model is
accompanied by a handshake validation signal. In the corresponding
hardware, every data-carrying bus has a companion net that carries a
status indicator. Under different circumstances the status indicator may be set to
invalid. For example, a pipeline might not yet have filled, or outputs might be bursty,
as with an FFT. This block simply reports the valid status of the samples presented to
it.
There are no parameters for this block.