Fluke PM6681R, PM6685R manual Initialization and Resetting, Reset Strategy, Bus Initialization

Introduction to SCPI

Initialization and Resetting

Reset Strategy

There are three levels of initialization:

–Bus initialization

–Message exchange initialization

–Device initialization

￿Bus Initialization

This is the first level of initialization. The controller program should start with this which initializes the IEEE-interfaces of all connected instruments. It puts the complete system into remote enable (REN-line active) and the controller sends the interface clear (IFC) command. The command or the command sequence for this initialization is controller and lan- guage dependent. Refer to the user man- ual of the system controller in use.

￿Message Exchange Initialization

Device clear is the second level of initial- ization. It initializes the bus message ex- change, but does not affect the device functions.

Device clear can be signaled either with DCL to all instruments or SDC (Selective device-clear) only to the addressed instru- ments. The instrument action on receiv- ing DCL and SDC is identical, they will do the following:

–Clear the input buffer.

–Clear the output queue.

–Reset the parser.

–Clear any pending commands.

The device-clear commands will not do the following:

–Change the instrument settings or stored data in the instrument.

–Interrupt or affect any device operation in progress.

–Change the status byte register other than clearing the MAV bit as a result of clearing the output queue.

￿ Many older IEEE-instruments, that are not IEEE-488.2 compati- ble returned to the power-on de- fault settings when receiving a device-clear command. IEEE-488.2 does not allow this.

When to use a Device-clear Command

The command is useful to escape from erroneous conditions without having to alter the current settings of the instru- ment. The instrument will then discard pending commands and will clear re- sponses from the output queue. For ex- ample; suppose you are using the Counter in an automated test equipment system where the controller program returns to its main loop on any error condition in the system or the tested unit. To ensure that no unread query response remains in the output queue and that no unparsed message is in the input buffer, it is wise to use device-clear. (Such remaining re- sponses and commands could influence later commands and queries.)

￿Device Initialization

The third level of initialization is on the device level. This means that it concerns only the addressed instruments.

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