Configuring the Crosspoint Switch Module

The Crosspoint Switch module can be configured after placement on the schematic sheet using the Crosspoint Switch Configuration dialog (Figure 1). To access this dialog, simply right-click over the symbol for the device and choose the Configure command from the context menu that appears. Alternatively, click on the Configure button available in the Component Properties dialog for the device.

Figure 1. Configuration dialog for the Crosspoint Switch module.

Use the dialog to configure the device as required. Essentially, you need to configure three areas:

• The signal block structure

• The input and output blocks

• How the input and output blocks are connected.

The following sections take a closer look at these three areas.

Defining Signal Block Structure

The Block Structure region of the dialog enables you to define the set of signals that are received by the instrument at its input blocks and channeled through to its output blocks. This signal structure is common to each input and output block. Simply click the associated Add button for the region to add a signal to the structure.

Click on the entry for a signal to edit the default signal name and replace it with a more meaningful name. Set the width of the signal – in terms of bits – as required. Although the width specified can be any number of bits, this will typically be kept to 8, 16 or 32 bits.

Use the Move Up and Move Down buttons to control the order of the signals within the structure, as they will appear on the schematic symbol.

Defining Input and Output Blocks

Use the Add buttons available to the left and right of the Blocks & Connections region of the dialog to add input and output blocks for the instrument respectively. You can add any number of input and output blocks. As you add a new block its field will become editable, should you wish to enter a custom name for it.

The blocks will appear on the left (inputs) and right (outputs) of the symbol for the device on the schematic, and also in the device's associated instrument panel. The graphical order of blocks can be changed using the associated Move Up and Move Down buttons for each side. Ensure that the block you wish to move is first selected.

Should you wish to delete a block, simply select it and click on the corresponding Remove button.

Connecting the Blocks

Once the block signal structure has been defined and the number of input and output blocks added as per design requirements, it is time to define the initial interconnections between the blocks. These initial connections will be used by the instrument after downloading the design to the target physical FPGA device.

A connection itself specifies how external input signals arriving at an input block are routed internally by the instrument, to appear at an output block. Put simply, it determines which input is connected to which output. You can connect an input block to one or more output blocks. You can also leave input or output blocks unconnected. In the latter case, they will retain and output their previous value, in cases where they have had a prior connection to them.

To add a connection, simply click on the Add Connection button, beneath the list of defined I/O blocks. You will be prompted to click on an output block that is currently unconnected. Having done this, you will be prompted to click on an input block. Once this is done, a graphical connection will appear, linking the nominated input and output blocks.

Figure 2. Connecting AIN to COUT.

To remove a connection, simply click on the Remove Connection button. You will be prompted to click on an output block that is currently connected. Click on the block associated with the connection you wish to delete – the graphical connection will be removed.