Specifications

Appendix B 559
GPIB Status Report System
General Model of Status Registers
B. GPIB Status Report System
Transition Filter and Condition Register
The E4991A status transition filter allows the user to select the transition direction of a
bit’s status in the status register, which sets the bit in the event register.
If the status register has transition filters, a lower level register called “condition register”
exists under the event register. The transition filer lies between the event register and the
condition register. The transition filter allows the corresponding event register bit to be set
according to the positive transition, negative transition, or both of a bit in the condition
register. For example, when a negative transition filter is set, if a negative transition has
occurred in a bit of a condition register, that is, a bit in the condition register has changed
from 1 to 0, the corresponding bit in the event register of the upper level is set to 1.
Figure B-2 Status Transition Filter and Condition Register
In the E4991A, the Operation Status Register and the Questionable Status Register have
transition filters (
Figure B-3). By monitoring status transition in bit 4 of the Operation
Status Register, transition filters allow generation of an SRQ when the E4991A starts or
stops measurement.