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Example:
The counter answers 40 when you ask for
the contents of the Standard Event Status
Register.
–
Convert this to binary form. It will give
you 101000.
–
Bit 5 is true showing that a command error
has occurred.
–
Bit 3 is also true, showing that a device de
-
pendent error has occurred.
Use the same technique when you pro
-
gram the enable registers.
–
Select which bits should be true.
–
Convert the binary expression to decimal
data.
–
Send the decimal data to the instrument.
Clearing/Setting all bits
–
You can clear an enable register by pro-
gramming it to zero. You can set all bits
true in a 16-bit event enable register by
programming it to 32767 (bit 16 not used).
–
You set all bits true in 8-bit registers by
programming them to 255 (Service Re
-
quest Enable and Standard Event Enable.)
n
Using the Queues
The two queues, where CNT-8X stores
output data and error messages, may con
-
tain data or be empty. Both these queues
have their own status bit in the Status
Byte. If this bit is true there is data to be
fetched.
When the controller reads data, it will
also remove the data from the queue. The
queue status bit in the status byte will re
-
main true for as long as the queue holds
one or more data bytes. When the queue
is empty, the queue status bit is set false.
Status of the Output Queue (MAV)
The MAV (message available) queue sta
-
tus message appears in bit 4 of the status
byte register. It indicates if there are bytes
ready to be read over the GPIB in the
GPIB output queue of the instrument.
The output queue is where the formatted
data appears before it is transferred to the
controller.
The controller reads this queue by ad
-
dressing the instrument as a talker. The
command to do this differs between dif
-
ferent programming languages. Examples
are IOENTERS and IBREAD.
Status of the Error Message Queue
(EAV)
The EAV (error message available)
queue status message appears in bit 2 of
the status byte register. Use the
:SYSTem:ERRor? query to read the er-
ror messages. Chapter 21 explains all
possible error messages .
n
Using the Status Byte
The status byte is an eight bit status mes
-
sage. It is sent to the controller as a re
-
sponse to a serial poll or a *STB? query,
see Figure 6-7. Each bit in the status byte
contains a summary message from the
status structure. You can select what bits
in the status byte should generate a ser
-
vice request to alert the controller.
When a service request occurs, the
SRQ-line of the GPIB will be activated.
Whether or not the controller will react
on the service request depends on the
controller program. The controller may
be interrupted on occurrence of a service
6-16 Status Subsystem
Using the Subsystems