Tektronix Keithley 2651A Reference Manual page 891

Section 15: Status model
•
Positive Transition Register (PTR) (.ptr): When a bit is set in this read-write register, it
enables a 0 to 1 change in the corresponding bit of the condition register to cause the
corresponding bit in the event register to be set.
An event is represented by a condition register bit changing from a 1 to 0 or 0 to 1. When an event
occurs and the appropriate NTR or PTR bit is set, the corresponding event register bit is set to 1. The
event bit remains latched to 1 until the event register is read or the status model is reset. When an
event register bit is set and its corresponding enable bit is set, the summary bit of the register is set
to 1. This, in turn, sets a bit in a higher-level condition register, potentially cascading to the associated
summary bit of the Status Byte Register.
Queues
The Model 2651A uses queues to store messages. The queues include:
•
Command queue: Holds commands that are available for execution.
•
Output queue: Holds response messages.
•
Error queue: Holds error and status messages.
When a queue contains data, it sets the condition bit for that queue in one of the registers. The
condition bits are:
•
Command queue: CAV in the Operation Status Remote Summary Register
•
Output queue: MAV in the Status Byte Register
•
Error queue: EAV in the Status Byte Register
The CAV, MAV, and EAV bits in the registers are cleared when the queue is empty. Queues
empty when:
•
Commands are executed
•
Errors are read from the error queue
•
Response messages are read from the instrument
All Model 2651A queues are first-in, first-out (FIFO).
The Status byte and service request enable registers
structured with the other registers.
15-2
Model 2651A High Power System SourceMeter® Instrument Reference Manual
(on page 15-5) shows how the queues are
2651A-901-01 Rev. C October 2021