Table of Contents
Advertisement
RQS/MSS
The original status byte of IEEE 488.1 is sent as a response to a serial poll, and bit 6
means requested service, RQS.
IEEE 488.2 added the *STB? query and expanded the status byte with a slightly different
bit 6, the MSS. This bit is true as long as there is unfetched data in any of the status event
registers.
•
The Requested Service bit, RQS, is set true when a service request has been signaled.
If you read the status byte via a Serial Poll, bit 6 represents RQS. Reading the status
byte with a serial poll will set the RQS bit false, showing that the status byte has been
read.
•
The Master Summary Status bit, MSS, is set true if any of the bits that generates SRQ
is true. If you read the status byte using *STB?, bit 6 represents MSS. MSS remains
true until all event registers are cleared and all queues are empty.
Setting up the Instrument to Report Status
To use the status reporting feature, include the following steps in your program.
*CLS clears all event registers and the error queue.
*ESE <bit mask> selects what conditions in the Standard Event Status register
should be reported in bit 5 of the status byte.
:STATus:OPERation:ENABle <bit mask> selects which conditions in the
Operation Status register should be reported in bit 7 of the status byte.
:STATus:QUEStionable:ENABle <bit mask> selects which conditions in the
Questionable Status register should be reported in bit 3 of the status byte.
*SRE <bit mask> selects which bits in the status byte should cause a Service
Request.
Reading and Clearing Status
Status Byte
There are two way to read the status byte register: Using the Serial Poll and using the
Common Query.
Using the Serial Poll (IEEE-488.1 defined)
Response:
•
Bit 6: RQS message shows that the Instrument has requested service via the SRQ
signal.
•
Other bits show their summary messages
•
A serial poll sets the RQS bit FALSE, but does not change other bits.
Using the Common Query *STB?
Response:
•
Bit 6: MSS message shows that there is a reason for service request.
•
Other bits show their summary messages.
•
Reading the response will not alter the status byte.
SCPI and IEEE Bus Descriptions
Status Reporting System
4B
4B-19
Advertisement
Table of Contents
