14-3
IM 2558A-01EN
Status Reports
3
2
1
4
5
6
7
8
9
10
11
12
13
14
15
16
App
Index
14.2 Status Byte
Status Byte Operation
A service request is issued when bit 6 in the status
byte becomes 1. Bit 6 is set to 1 when any other bit
becomes 1 (when the corresponding bit of the service
request enable register is also set to 1). For example,
if an event occurs and the logical OR of a standard
event register bit and its corresponding enable register
bit is 1, then bit 5 (ESB) is set to 1. At this point, if bit 5
of the service request enable register is 1, bit 6 (MSS)
is set to 1, and the 2558A requests service from the
controller.
You can check what type of event occurred by reading
the contents of the status byte.
Reading the Status Byte
There are two ways to read the contents of the status
byte.
• *STB? Query
Bit 6 functions as MSS when a query is made using
*STB?
. This causes the MSS to be read. This query
does not cause any of the status byte bits to be
cleared after the status byte is read.
• Serial Polling
Serial polling causes bit 6 to function as an RQS bit.
This causes the RQS to be read. After the status
byte is read, only the RQS bit is cleared. You cannot
read the MSS bit when serial polling is used.
Clearing the Status Byte
There is no way to clear all the bits in the status byte.
The bits that are cleared for each operation are shown
below.
• *STB? Query
None of the bits are cleared.
• Serial Polling
Only the RQS bit is cleared.
• When a *CLS Command Is Received
When a
*CLS
command is received, the status byte
itself is not cleared, but the contents of the standard
event register, which affects the bits in the status
byte, are cleared. As a result, the corresponding
status byte bits are cleared. Because the output
queue is not cleared with a
*CLS
command, bit 4
(MAV) in the status byte is not affected. However,
the output queue will be cleared if the
*CLS
command is received just after a program message
terminator.
Status Byte
7
6 ESB MAV EES EAV 1
0
RQS
MSS
• Bits 0, 1, and 7
Not used (always 0)
• Bit 2 EAV (Error Available)
This bit is 1 when the error queue is not empty. In
other words, this bit is set to 1 when an error occurs.
See section 14.5.
• Bit 3 EES (Extend Event Summary Bit)
This bit is set to 1 when the logical AND of the
extended event register and the extended event
enable register is 1. In other words, this bit is set
to 1 when a certain event takes place inside the
instrument. See section 14.4.
• Bit 4 MAV (Message Available)
This bit is 1 when the output queue is not empty. In
other words, this bit is set to 1 when there is data to
be transmitted in response to a query. See section
14.5.
• Bit 5 ESB (Event Summary Bit)
This bit is set to 1 when the logical AND of the
standard event register and the standard event
enable register is 1. In other words, this bit is set
to 1 when a certain event takes place inside the
instrument. See section 14.3.
• Bit 6 RQS (Request Service)/MSS (Master Status
Summary)
This bit is 1 when the logical AND of the status
byte excluding bit 6 and the service request enable
register is 1. In other words, this bit is set to 1 when
the instrument requests service from the controller.
RQS is set to 1 when the MSS bit changes from 0 to
1 and is cleared when serial polling is carried out or
when the MSS bit changes to 0.
Bit Masking
To mask a bit in the status byte so that it does not
cause an SRQ, set the corresponding bit of the service
request enable register to 0.
For example, to mask bit 2 (EAV) so that service is not
requested when an error occurs, set bit 2 of the service
request enable register to 0. Do this using the
*SRE
command. To query whether each bit of the service
request enable register is 1 or 0, use
*SRE?
. For
details on the
*SRE
command, see chapter 13.
