*OPC? — Operation Complete Query Place a “1” in the output queue after all
pending operations are completed
Description
On power-up or when the *CLS or *RST is executed, the Model 2016 goes into the Operation
Complete Command Query Idle State (OQIS). In this state, no pending overlapped commands
exist. The Model 2016 has three overlapped commands:
• :INITiate
• :INITiate:CONTinuous ON
• *TRG
When you send the *OPC? command, the Model 2016 exits from OQIS and enters the
Operation Complete Command Query Active State (OQAS). In OQAS, the instrument
continuously monitors the No-Operation-Pending flag. After the last pending overlapped
command is completed (No-Operation-Pending flag set to true), an ASCII character “1” is
placed into the Output Queue, the Message Available (MAV) bit in the Status Byte sets, and the
instrument goes back into OQIS. Addressing the Model 2016 to talk sends the ASCII “1” to the
computer.
Note that the instrument always goes into OQAS when *OPC? is executed. If no pending
command operations are present (e.g. trigger model in idle state), the Model 2016 immediately
places an ASCII “1” in the Output Queue, sets the MAV bit and returns to OQIS.
When used with the :INITiate or :INITiate:CONTinuous ON command, an ASCII “1” will
not be sent to the Output Queue and the MAV bit will not set until the Model 2016 goes back
into the idle state. The initiate operations are not considered finished until the instrument goes
into the idle state.
When used with the *TRG command, an ASCII “1” will not be placed into the Output Queue
and the MAV bit will not set until the operations associated with the *TRG command (and the
initiate command) are finished. The *TRG command is considered to be finished when the
Device Action completes or when operation stops at a control source to wait for an event (see
the Trigger Model in this section).
To use *OPC? exclusively with the *TRG command, first force the completion of the initiate
command so that only the *TRG command is pending. To do this, send the :ABORt command
to place the instrument in idle, which (by definition) completes the initiate command. Since
continuous initiation is on, operation continues on into the Trigger Model. After sending the
*TRG command, an ASCII “1” is placed in the Output Queue and the MAV bit sets when the
*TRG command is finished.
After *OPC? is executed, additional commands cannot be sent to the Model 2016 until the
pending overlapped commands are finished. For example, :INITiate:CONTinuous ON followed
by *OPC? locks up the instrument and requires a device clear (DCL or SDC) before it will
accept any more commands.
NOTE See *OPC, *TRG and *WAI for more information.
4-40 Remote Operation
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