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2600AS-901-01 Rev. B / September 2008
Appendix C: Status Model
Series 2600A System SourceMeter® Instruments Reference Manual
Overview
The Keithley Instruments Series 2600A System SourceMeter
®
instrument provides a number of
status registers and queues, allowing the operator to monitor and manipulate the various
instrument events. The status model is shown in
. The heart of the
status model is the Status Byte Register. This register can be read by the user's test program to
determine if a service request (SRQ) has occurred, and what event caused it.
Status byte and SRQ
The Status Byte Register receives the summary bits of five status register sets and two queues.
The register sets and queues monitor the various instrument events. When an enabled event
occurs, it sets a summary bit in the Status Byte Register. When a summary bit of the Status Byte is
set and its corresponding enable bit is set (as programmed by the user), the RQS/MSS bit will set
to indicate that an SRQ has occurred.
SRQs will affect both the GPIB and the VXI-11 connections. On the GPIB, the SRQ line will be
asserted. On a VXI-11 connection, an SRQ event will be generated.
Status register sets
A typical status register set is made up of a condition register, an event register, an event enable
register, a negative transition register, and a positive transition register. A condition register is a
read-only register that constantly updates to reflect the present operating conditions of the
instrument.
When an event occurs, and the appropriate NTR or PTR bit is set, the matching event register bit
is set to 1. The bit remains latched to 1 until the register is reset. When an event register bit is set
and its corresponding enable bit is set (as programmed by the user), the output (summary) of the
register will set to 1. This in turn sets the condition bit in a higher-level register, and can ultimately
cascade to a summary bit of the Status Byte Register.
Queues
The SourceMeter instrument uses an Output Queue and an Error Queue. The response
messages, such as requested readings, are placed in the Output Queue. As various 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 Queue;
MAV for the Output Queue).
