Appendix E: Status model
Model 2657A High Power System SourceMeter® Instrument Reference Manual
E-2
2657A-901-01 Rev. B/December 2012
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 2657A 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 2657A queues are first-in, first-out (FIFO).
The
Status byte and service request enable registers
(on page E-6) shows how the queues are
structured with the other registers.
Command queue
The command queue holds commands that have been received from a remote interface that are
available for execution. This allows the Model 2657A to accept multiple commands and queue them
for execution.
When a command is received from a remote interface, the command available (CAV) bit in the
Operation Status Remote Summary Register is set. For additional detail, see
(on page 7-293).
Output queue
Response messages, such as those generated from print commands, are placed in the output queue.
All remote command interfaces share the same output queue.
The output queue sets the message available (MAV) bit in the status model.
The data in the output queue is cleared by the
*CLS
command.
Summary of Contents for 2657A
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