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Hardware Configuration of a RS-232/RS-485 SCXI System

Hardware: SCXI

Problem: What are the necessary hardware configurations to consider when setting up a Remote SCXI system?

Solution:

Since the data from the SCXI chassis is passed back to the computer via a serial link, the analog inputs and outputs to the remote SCXI system require digitization within the chassis itself. This is the reason why an SCXI-1200 DAQ module is required in the remote chassis. The configuration steps are shown below.

Configuration of SCXI-1200

The majority of the settings for the SCXI-1200 can be changed from the Measuremnt and Automation Explorer (MAX) and as such do not require you to open the module casing. However if you are using the SCXI-1200 with other SCXI modules, then jumper W1 must be set in the correct position.

Jumper W1 should be placed in the position A-B if the module is being used on its own. Note that this is the factory default setting.
If the module is being used with other SCXI modules, then W1 should be placed in the position B-C. Refer to the SCXI-1200 User Manual for further details.

Configuration of other SCXI modules

If you are using additional SCXI modules within your remote chassis, be aware that many of the modules require jumpers on the board to be changed if the module is to operated in a configuration other than that intended with the factory-default settings. Refer to the User Manual of the module in question for further information.

Configuration of SCXI-2000

Full details regarding the configuration of the SCXI-2000 chassis can be found in the User Manual. You will need to make a note of the HDLC address and the baud rate for the chassis, as this will be required when configuring the system using MAX.

You will next need to connect the SCXI-1200 module to the SCXI-2000 chassis. The SCXI-1200 DAQ module should be inserted into the left-hand slot (slot 1). Connect the 25-pin end of your short parallel port cable to the parallel port connector on the back of the SCXI-1200 module. Then connect the 36-pin end of your parallel port cable to the parallel port connector on the back of the SCXI-2000 chassis. See diagram below:

Configuration of SCXI-2400

Full details regarding the configuration of the SCXI-2400 module can be found in the User Manual. You will need to make a note of the HDLC address and the baud rate for the chassis, as this will be required when configuring the system using MAX.

If you are using an SCXI-1200 DAQ module, install the SCXI-1200 in the slot adjacent to the SCXI-2400 and connect the 25-pin end of your short parallel port cable to the parallel port connector on the DAQ module. Then connect the 36-pin end of your parallel port cable to the parallel port connector on the back of the SCXI-2400 adapter board. See diagram below.

Important Note: Do not attempt to remove any SCXI module from the chassis while it is still powered up. Failure to switch off the chassis may cause damage to the module being removed.

Cabling Considerations

Communicating to a remote SCXI system using RS-232 requires a null modem cable to be used between the host PC and the chassis. Also, the RS-485 connector on the SCXI-2000/2400 uses a screw terminal plug to accept wires from your RS-485 cable. Use twisted pair cable to increase noise tolerance. Make the network connections as given in the table below:

Computer RS-485 Port	SCXI-2000/2400
TX+	RX+
TX-	RX-
RX+	TX+
RX-	TX-

It is recommended that termination resistors are used at both ends of the RS-485 link. For twisted pair cable, 120W resistors are sufficient. Refer to either the SCXI-2000 or SCXI-2400 User Manual for further details.

Now that you are familiar with the hardware configuration, you can proceed to one of the links below to complete your understanding of setting up a remote SCXI system or return to Configuring a RS-232/RS-485 SCXI System.

Once you are familiar with the steps necessary to use your remote SCXI system, feel free to visit our SCXI & Signal Conditioning Support page for additional documentation.

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