GPIB Drivers :: GPIB I/O Support (xPC Target™)

The xPC Target software interfaces the target PC to a GPIB instrument bus using an external GPIB controller from National Instruments. This external controller is connected to the target PC with a serial cable.

The xPC Target software uses a model for I/O that includes both Simulink blocks, for the I/O drivers, and MATLAB structures for sequencing messages and commands. This model provides increased flexibility and control over using only Simulink blocks in your model.

Hardware Connections for GPIB

The xPC Target software supports connecting to a GPIB instrument bus with a GPIB-232CT-A controller from National Instruments.

One end of the controller is connected to either the COM1 or COM2 port on the target PC with a null modem cable. The other end is connected to the GPIB instrument bus with a standard GPIB connector and cable.

Simulink Blocks for GPIB

To support the use of GPIB, the xPC Target I/O library includes a set of GPIB driver blocks. These driver blocks can be added to your Simulink model to provide inputs and outputs to devices on a GPIB instrument bus.

GPIB Setup — One setup block is needed for each GPIB controller. The setup block does not have any inputs or outputs, but sends the initialization and termination messages.
GPIB Send/Receive — The send/receive block has inputs and outputs from your Simulink model, and sequences both the send and receive messages.

MATLAB Message Structures for GPIB

Communication is through a series of messages passed back and forth between the target PC and the GPIB controller. To accomplish this, the messages sent to the GPIB controller must be in a format that the controller understands. Likewise, the target PC must know how to interpret the data returned from the GPIB controller.

xPC Target uses MATLAB structures to create messages and map the input and output ports on the GPIB driver blocks to the data written and read from the GPIB devices. The GPIB Setup block executes the messages in the initialization structure after downloading the target application. The GPIB Send/Receive block repeats the execution of the messages in the send/receive structure during each sample interval. When the target application stops running, the GPIB Setup block executes the messages in the termination structure.

Below is an example of a send/receive message structure. The first message writes a command to instruct the GPIB device to acquire a single data value, while the second message sends a command to read that value and output the result to the output port line coming from a GPIB driver block.

Currently, only two limitations exist. The xPC Target software does not support string data types as input and output data types. Also, you must know the size and order of data returned from a read command.

For more information on this example, see Creating GPIB Message Structures.

GPIB I/O Support

Using GPIB Drivers

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