Status Of The Output Queue (Mav); Using The Status Byte; Selecting Summary Message To Generate Srq - Fluke 9640A Series Instruction Manual

9640A
Instruction Manual
Use the same technique when you program the enable registers.
1. Select which bits should be true.
2. Convert the binary expression to decimal data.
3. Send the decimal data to the instrument.
Clearing/Setting all bits
Clear an enable register by programming it to zero. To set all bits true in a 16-bit event
enable register program it to 32767 (bit 16 not used).
To set all bits true in an 8-bit registers program it to 255 (Service Request Enable and
Standard Event Enable.)

Status of the Output Queue (MAV)

The MAV (message available) queue status 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 addressing the instrument as a talker.

Using the Status Byte

The status byte is an eight-bit status message. It is sent to the controller as a response to a
serial poll or a *STB? query. 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
service 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 request, it may regularly test the
SRQ-line, it may regularly make serial poll or *STB?, or the controller may not react at
all. The preferred method is to use SRQ because it presents a minimum of disturbance to
the measurement process.

Selecting Summary Message to Generate SRQ

The Instrument does not generate any SRQ by default. You must first select which
summary message(s) from the status byte register should give SRQ. You do that with the
Service Request Enable command *SRE <bit mask>.
Example
This sets bit 4 (16=00010000
instrument signal SRQ when a message is available in the output queue.
4B-18
*SRE 32
) in the service request enable register. This makes the
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