IEEE-488 Reference
3-140
When storage starts, the ARM indicator turns on to denote that raw input readings are being
stored in the buffer. After the storage process is finished, the * indicator turns on to denote that
post processing (i.e. math calculations) is being performed on the readings. When post process-
ing is finished, the * indicator turns off and the instrument returns to the idle state. The Trace
subsystem is used to read the buffer.
Sending a bus command to the Model 2002 while raw readings are being acquired aborts the
acquisition and post processes the readings already stored in the buffer.
ASTReam and SSTReam
These two “stream” parameters are used to send “fresh” A/D readings over the IEEE-488 bus at
maximum speed. The ASTReam parameter is used to send readings in the ASCII format, and
the SSTReam parameter is used to send readings in the Single Integer (counts) format. The
stream modes can be used for the following functions: DCV, ACV (average and RMS), DCI,
ACI (average and RMS) and Ω2. TEMP, FREQ, Ω4, in-circuit current, and peak measurements
cannot be used with stream mode.
With ASTReam, up to 1000 readings per second can be sent over the bus, and with SSTReam,
up to 2000 readings per second can be sent. Once the Model 2002 is placed in a stream mode,
one A/D reading is sent over the bus every time the instrument is addressed to talk.
ASCII stream mode:
With ASTReam, only the reading is sent. All other data elements (units, reading number, time
stamp, etc.) are not included.
A line feed (LF) with EOI is used as a terminator for each reading. An overflowed reading is
returned as a +/-30,000 count reading. For example, a 10kΩ resistor being measured on the 2kΩ
range will return the following overranged reading:
+3.0000E+03 (Overranged ASTReam reading)
Single integer stream mode:
The SSTReam mode sends single precision integer readings. Each reading is 2-bytes in size and
is not terminated by a line feed (LF). EOI is asserted with the second byte of each reading.
With SSTReam, only the number of A/D counts are sent. For example, a 1.5V reading on the
2V range will be sent as follows:
15000
The same reading (1.5V) on the 20V range is sent as follows:
1500
An overrange reading is expressed as +/-30,000 counts. For example, if a 50kΩ resistor is mea-
sured on the 20kΩ range, the overranged reading will be expressed as follows:
30000 (Overranged SSTReam reading)
Operating considerations:
Before going into a stream mode, make sure the instrument is on the desired function and range.
Once in a stream mode, all front panel controls are disabled, and all SCPI and Common com-
mands are ignored.
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