Using the SCXI-1129 as 1-wire Matrix

This document discusses methods of using the SCXI-1129, 256 cross-point, 2-wire matrix for 1-wire application.

Introduction

There are many matrix applications that do not require the use of differential (2-wire), switching systems. For cases where ground referenced measurements or non-differential, two point measurements are to be made, a 1-wire matrix may be better suited. It is possible, however, to use a 2-wire matrix as a 1-wire matrix. This may be desirable because:

· Differential matrices were already being used elsewhere and are available.
· Using a 2-wire matrix in 1-wire doubles the column and row count.
· Other parameters such as voltage or current rating are required but not obtainable in a 1-wire matrix.

Basics

The simplest method of using a 2-wire matrix in 1-wire mode is to merely use half of the rows and half of the columns. If you use the SCXI-1129 with the SCXI-1334 (4x64 2-wire terminal block), you will have a 4x64 1-wire matrix.

2x124 1-wire Matrix: Instrument on Rows, DUTs on Columns

A common usage is to connect 2-wire instruments to the rows and measure/stimulate DUTs on the columns. This will allow you to connect 2 instruments simultaneously to any of the 64 columns.
If your application requires only one differential instrument, you could route up to 124 signals connected to the columns to the instrument.
Figure 1 illustrates the connection setup. The instrument is connected to only 1 lead of row 0 and 1, the DUTs are connected to columns 0 to 61, and rows 2, row 3, column 62, and column 63 are used to connect any column + and - to any row - and + respectively. The ability to swap polarities allows the use of both the “+” and “-“ column. With an instrument connected between rows 0 and 1, there are now 124 columns available for connections to DUT points.


In order to use the SCXI-1129 for a 1-wire application, two connections must first be made within the SCXI-1334 terminal block. These are:

Connect r2+ to c62- to allow connection of any “+” column to any “-“ row.
Connect r3- to c63+ to allow connection of any “-” column to any “+“ row.

r2+ to c62- Connection:
This configuration connection provides the “-” rows with access to any of the available 62 “+“ columns. Note that c62+ and r2- are not connected (NC). This prevents short circuits from occurring when routing signal through r2+ and c62-.

r3- to c63+ Connection:
This configuration connection provides the “+” rows with access to any of the available 62 “-“ columns. Note that c63- and r3+ are not connected (NC). This prevents short circuits from occurring when routing signal through r3- and c63+.

Configuration Summary

· r2, r3, c62 and c63 are not used for matrix connections (NC: no connect)
· r0- and r1+ are not used for matrix connections (NC: no connect)
· c0 ± though c61 ±, r0+, and r1- are used for 1-wire matrix connections.

Matrix Connections

The 1-wire matrix that remains after configuration is 2x124, or 248 cross-points. Connections to this matrix are made via the rows at r0+ and r1- and the columns starting at c0± through c61±. Figure 2 shows the original 4x64 2-wire matrix re-mapped for 1-wire usage.

• Connections that do not require swapping of line polarities are made in the normal fashion. Simply connect the desired row to the desired column:

To connect any “+” column to r0+, activate the corresponding row/column relay.
To connect any “-“ column to r1-, activate the corresponding row/column relay.

• Connections that require swapping of line polarities are made as follows:

To connect a specific “+” column to r1-, activate the r2 specific column relay and the r1/c62 relay.
To connect a specific “-“ column to r0+, activate the r3/specific column relay and the r0/c63 relay.

Example

The SCXI-1129 configured for a 1-wire application can be used to measure voltages between any 2 points of a DUT. This application is illustrated in figure 3.
To measure voltages between c0 and c1 of the 1-wire matrix, execute the following operation using the 2-wire row and column names:
Connect c0 to r0, and c0 to r1

To measure voltages between c0 and c2:
Connect c0 to r0, c1 to r2, and c62 to r1

To measure voltages between c1 to c3:
Connect c0 to r3, c63 to r0, and c1 to r1

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