Keithley 2000, User Manual, Page: 132 / 280

*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 2000 goes into the Operation
Complete Command Query Idle State (OQIS). In this state, no pending overlapped commands
exist. The Model 2000 has three overlapped commands:
• :INITiate
• :INITiate:CONTinuous ON
• *TRG
When you send the *OPC? command, the Model 2000 exits from OQIS and enters the Oper-
ation Complete Command Query Active State (OQAS). In OQAS, the instrument continuously
monitors the No-Operation-Pending flag. After the last pending overlapped command is com-
pleted (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 2000 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 2000 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 2000 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 De-
vice 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 con-
tinuous 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 2000 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 ac-
cept any more commands.
Note: See *OPC, *TRG and *WAI for more information.
4-46 Remote Operation