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Detecting Measurement Events In The 2001
Instruments that complied with the IEEE-488.1 standard used a Serial Poll
Byte to return important information about internal functions of the
instrument. The 2001 on the other hand, which complies with the IEEE-488.2
standard, no longer uses a Serial Poll byte. It contains many status
registers. These registers include a Standard Event, Operation Event, Arm
Event, Sequence Event, Trigger Event, Measurement Event, and a Questionable
Event register. There is also a Status Byte register which is used to
summarize the status of a few of the previously mentioned event status
registers. The status byte register of the 2001 should not be confused with
the status byte register used on IEEE-488.1 compliant instruments.
The Measurement Event Status Register is a latched, 16-bit read-only
register whose bits are set by the Measurment Event Condition register
and Transition filter. Once a bit is set, it will remain set until the
register is cleared by a specific operation.
The Measurement Event Status Register is composed of the following
conditions:
Bit 11 Buffer Pretriggered Weighted value = 2048
Bit 10 Buffer Overflow Weighted value = 1024
Bit 9 Buffer Full Weighted value = 512
Bit 8 Buffer Half Full Weighted value = 256
Bit 7 Buffer Available Weighted value = 128
Bit 6 Voltmeter Complete Weighted value = 64
Bit 5 Reading Done Weighted value = 32
Bit 4 High Limit 2 Weighted value = 16
Bit 3 Low Limit 2 Weighted value = 8
Bit 2 High Limit 1 Weighted value = 4
Bit 1 Low Limit 1 Weighted value = 2
Bit 0 Reading Overflow Weighted value = 1
These bits generally will provide the most usable information that a user
will need. As an example, suppose the 2001 is collecting data into the data
buffer and you would like to know when the buffer is full. To permit the
Measurement Event Status register to latch the Buffer Full bit, the
Measurement Event Positive Transition Filter must be masked such that when
the rising edge of the Buffer Full bit of the Measurement Event Condition
register occurs, the Buffer Full bit in the Measurement Event Status register
is latched. A complete figure of the Measurement Event Status registers is
attached to help understand the process. The example code below illustrates
this example ( code is written using the CEC format ):
'** Set Positive &NegativeTransition Filters here, send *CLS to clear
'** status model
cmd$ = ":Status:Measure:Ptransition 512; Ntransition 0"
Call Send(GPIBAddress, cmd$, status%)
cmd$ = "*CLS"
Call Send(GPIBAddress, cmd$, status%)
'
'***Code to start reading process is placed here
'
'**** Check for Buffer Full here
Do
cmd$ = ":Status:Measure:Event?" 'Query Measure Event Status
Call Send(GPIBAddress, cmd$, status%)
Call Enter(Event$, 10, l%, GPIBAddress, status%)
Loop Until (Val(Event$) AND 512) = 512 'Loop until buffer full bit is set
'
'
This procedure can be applied to other events in the registers as well as
the other status registers available in the 2001. See the 2001 IEEE-488
Reference section for a complete breakdown of the 2001 Status Model.
John Tucker 5/3/92