Xilinx V2.1 manual SineCosine, Shift block parameters dialog box

Xilinx Blocks

Block Parameters Dialog Box

The block parameters dialog box can be invoked by double-clicking the icon in your Simulink model.

Figure 3-64: Shift block parameters dialog box

Parameters specific to the Shift block are:

∙Shift Direction: specifies a direction, Left or Right. The Right shift moves the input toward the least significant bit within its container, with appropriate sign extension. Bits shifted out of the container are discarded. The Left shift moves the input toward the most significant bit within its container with zero padding of the least significant bits. Bits shifted out of the container are discarded.

∙Number of Bits: specifies how many bits are shifted. If the number is negative, direction selected with Shift direction is reversed.

Other parameters used by this block are explained in the Common Parameters section of the previous chapter.

The Shift block does not use a Xilinx LogiCORE.

SineCosine

The Xilinx Sine Cosine block computes sin(x) and/or cos(x). It stores a reference sinusoid in a read-only memory (ROM), whose depth is defined by the width of the block’s single input port. An N-bit input address results in a logical ROM containing 2N equally spaced samples of one period (the implementation may actually store only a fraction of one

full period to reduce memory size). The input signal must be an unsigned integer.

The block can produce a sine or cosine (or its negative) at one output port, or both sine and cosine (or their negatives) at two output ports, depending on customization parameters. Stepping through the memory produces sampled sinusoids on the block’s output port(s), with output frequency determined by the address increment.

Although the error is quite small for practical choices of output width, the implementation is unbalanced; that is, values are stored in the memory as two’s complement numbers having exactly one sign bit. Consequently, sample values of the

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