14-43
IM 253421-01E
Communication Commands 2 (System of Commands Complying to the IEEE 488.2-1987 Standard)
14
Operation of the Status Byte
A service request is issued when bit 6 of the status
byte becomes “
1
”. Bit 6 becomes “
1
” when any of the
other bits becomes “
1
” (or when the corresponding bit
in the service request enable register becomes “
1
”).
For example, if an event takes place and the logical
OR of each bit of the standard event register and the
corresponding bit in the enable register is “
1
”, bit 5
(ESB) will be set to “
1
”. In this case, if bit 5 of the
service request enable register is “
1
”, bit 6 (MSS) will
be set to “
1
”, thus requesting service from the
controller.
It is also possible to check what type of event has
occurred by reading the contents of the status byte.
Reading from the Status Byte
The following two methods are provided for reading the
status byte.
• Inquiry using the *STB? query
Making an inquiry using the
*STB?
query sets bit 6 to
MSS. This causes the MSS to be read. After
completion of the read-out, none of the bits in the
status byte will be cleared.
• Serial poll
Execution of a serial poll changes bit 6 to RQS.
This causes RQS to be read. After completion of
the read-out, only RQS is cleared. Using a serial
poll, it is not possible to read MSS.
Clearing the Status Byte
No method is provided for forcibly clearing all the bits
in the status byte. Bits which are cleared are shown
below.
• When an inquiry is made using the *STB? query
No bit is cleared.
• When a serial poll is performed
Only the RQS bit is cleared.
• When the *CLS command is received
When the
*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 bits in the status byte are cleared,
except bit 4 (MAV), since the output queue cannot
be emptied by the
*CLS
command. However, the
output queue will also be cleared if the
*CLS
command is received just after a program message
terminator.
14.4.3 Standard Event Register
Overview of the Standard Event Register
URQ
6
PON
7
5
4
3
2
1
0
CME
EXE
DDE
QYE
RQC
OPC
Bit 7 PON (Power ON)
Bit 7 PON (Power ON) Set to “
1
” when power is turned
ON
Bit 6 URQ (User Request)
Not used (always “
0
”)
Bit 5 CME (Command Error)
Set to “
1
” when the command syntax is incorrect.
Examples: Incorrectly spelled command name; “
9
”
used in octal data.
Bit 4 EXE (Execution Error)
Set to “
1
” when the command syntax is correct but the
command cannot be executed in the current state.
Examples: Parameters are outside the setting range:
an attempt is made to make a hard copy during
acquisition.
Bit 3 DDE (Device Dependent Error)
Set to “
1
” when execution of the command is not
possible due to an internal problem in the instrument
that is not a command error or an execution error.
Bit 2 QYE (Query Error)
Set to “
1
” if the output queue is empty or if the data is
missing even after a query has been sent.
Examples: No response data; data is lost due to an
overflow in the output queue.
Bit 1 RQC (Request Control)
Not used (always “
0
”)
Bit 0 OPC (Operation Complete)
Set to “
1
” when the operation designated by the
*OPC?
command has been completed.
Bit Masking
To mask a bit in the standard event register so that it
does not cause bit 5 (ESB) of the status byte to
change, set the corresponding bit in the standard event
enable register to “
0
”.
For example, to mask bit 2 (QYE) so that ESB will not
be set to “
1
”, even if a query error occurs, set bit 2 of
the standard event enable register to “
0
”. This can be
done using the
*ESE?
command. To inquire whether
each bit of the standard event enable register is “
1
” or
“
0
”, use the
*ESE?
. For details of the
*ESE?
command,
see section 14.3.
14.4 Status Report
