Keithley 2600a series, Reference Manual, Page: 665 / 696

2600AS-901-01 Rev. B / September 2008 Return to Section Topics C-15
Series 2600A System SourceMeter® Instruments Reference Manual Appendix C: Status Model
• When using the *STB? common command or
status.condition
( Table C-3 ) to read
the status byte, B6 is the MSS bit.
• Bit B7, Operation Summary (OSB): Set summary bit indicates that an enabled operation
event has occurred.
Service request enable register
The generation of a service request is controlled by the Service Request Enable Register. This
register is programmed by the user and is used to enable or disable the setting of bit B6 (RQS/
MSS) by the Status Summary Message bits (B0, B2, B3, B4, B5, and B7) of the Status Byte
Register. As shown in
Figure C-10 , the summary bits are logically ANDed (&) with the
corresponding enable bits of the Service Request Enable Register. When a set (1) summary bit is
ANDed with an enabled (1) bit of the enable register, the logic “1” output is applied to the input of
the OR gate and, therefore, sets the MSS/RQS bit in the Status Byte Register.
The individual bits of the Service Request Enable Register can be set or cleared by using the
*SRE common command or its script equivalent. To read the Service Request Enable Register,
use the *SRE? query or script equivalent. The Service Request Enable Register clears when
power is cycled or a parameter value of 0 is sent with the *SRE command (i.e. *SRE 0). The
commands to program and read the SRQ Enable Register are listed in
Table C-3 .
Serial polling and SRQ
Any enabled event summary bit that goes from 0 to 1 will set bit B6 and generate an SRQ (service
request). In your test program, you can periodically read the Status Byte to check if an SRQ has
occurred and what caused it. If an SRQ occurs, the program can, for example, branch to an
appropriate subroutine that will service the request.
SRQs can be managed by the serial poll sequence of the SourceMeter instrument. If an SRQ does
not occur, bit B6 (RQS) of the Status Byte Register will remain cleared, and the program will simply
proceed normally after the serial poll is performed. If an SRQ does occur, bit B6 of the Status Byte
Register will set, and the program can branch to a service subroutine when the SRQ is detected by
the serial poll.
The serial poll automatically resets RQS of the Status Byte Register. This allows subsequent serial
polls to monitor bit B6 for an SRQ occurrence generated by other event types.
For common and script commands, B6 is the MSS (Message Summary Status) bit. The serial poll
does not clear MSS. The MSS bit stays set until all Status Byte summary bits are reset.
SPE, SPD (serial polling)
For the GPIB interface only, the SPE, SPD General Bus Command sequence is used to serial poll
the SourceMeter instrument (see
General bus commands ). Serial polling obtains the serial poll
byte (status byte). Typically, serial polling is used by the controller to determine which of several
instruments has requested service with the SRQ line.
Status byte and service request commands
The commands to program and read the Status Byte Register and Service Request Enable
Register are listed in
Table C-3 . Note that the table includes both common commands and their
script command equivalents. For details on programming and reading registers, see Programming
enable and transition registers and Reading registers .
To reset the bits of the Service Request Enable Register to 0, use 0 as the parameter value for the
command (for example, *SRE 0).