Appendix E: Status model
Model 2651A High Power System SourceMeter® Instrument Reference Manual
E-2
2651A-901-01 Rev. A / March 2011
Status register sets
Typically, a status register set contains the following registers:
•
Condition
(
.condition
): A read-only register that constantly updates to reflect the present
operating conditions of the instrument.
•
Enable Register
(
.enable
): A read-write register that allows a summary bit to be set when an
enabled event occurs.
•
Event Register
(
.event
): A read-only register that sets a bit to 1 when the applicable event
occurs. If the enable register bit for that event is also set, the summary bit of the register will set
to 1.
•
Negative Transition Register
(
.ntr
): A read-write register that when set to 1, specifies a
negative transition (change from 1 to 0) sets the event register bit.
•
Positive Transition Register
(
.ptr
): A read-write register that when set to 1, specifies a
positive transition (change from 0 to 1) sets the event register bit.
When an event occurs and the appropriate NTR or PTR bit is set, the matching event register bit is
set to 1. The event bit remains latched to 1 until the register is read or the status model is reset. When
an event register bit is set and its corresponding enable bit is set, the output (summary bit) of the
register will set to 1. This, in turn, sets a bit in a higher-level register cascading to the associated
summary bit of the Status Byte Register.
Queues
The High Power System SourceMeter
®
Instrument uses an output queue and an error or event
queue. Response messages, such as those generated from print commands, are placed in the output
queue. As programming errors and status messages occur, they are placed in the error queue. When
a queue contains data, it sets the appropriate summary bit of the Status Byte Register (EAV for the
error or event queue; MAV for the output queue).
The
(on page E-4) shows how the two queues are structured with the other
registers.
Service requests and connections
Service requests (SRQs) affect both the GPIB and the VXI-11 connections. On a GPIB connection,
the SRQ line is asserted. On a VXI-11 connection, an SRQ event is generated.
