IEEE-488 Reference
5-19
When reading the Status Byte Register using the *STB?
command, bit B6 is called the MSB bit. None of the bits in
the Status Byte Register are cleared when using the *STB?
command to read it.
The IEEE-488.1 standard has a serial poll sequence that will
also read the Status Byte Register and is better suited to de-
tect a service request (SRQ). When using the serial poll, bit
B6 is called the RQS bit. Serial polling causes bit B6 (RQS)
to reset. Serial polling is discussed in more detail later in this
paragraph (see “Serial Poll and SRQ”).
For description of the other bits in the Status Byte Register,
refer to paragraph 5.10.14.
The IEEE-488.2 standard uses the following common query
command that simply reads the Status Byte Register con-
tents:
*STB?
Figure 5-11
Status byte and service request (SRQ)
Status Summary Messages
* STB ?
Serial Poll
(B15 - B8)
OSB
(B7)
MSS
RQS
(B6)
ESB
(B5)
MAV
(B4)
QSB
(B3)
EAV
(B2) (B1) (B0)
OR
* SRE
* SRE ?
Status Byte
Register
Service Request
Enable Register
OSB = Operation Summary Bit
MSS = Master Summary Status (IEEE-488.2)
RQS = Request for Service (IEEE-488.1)
ESB = Event Summary Bit
MAV = Message Available
QSB = Questionable Summary Bit
EAV = Error Available
& = Logical AND
OR = Logical OR
(B15 - B8)
OSB
(B7) (B6)
ESB
(B5)
MAV
(B4)
QSB
(B3)
EAV
(B2) (B1) (B0)
&
&
&
&
&
0
0
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