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PACKed,16 format returns signed, 16-bit numbers preceded by the
ANSI/IEEE Standard 488.2-1987 Definite Length Arbitrary Block header
(Figure 3-11). Packed readings always represent a value between -1.0225
and +1.0230 or an overrange value, and must be converted (by the user) to
the actual reading value (see "Packed Reading Conversions").
REAL,64 format returns/retrieves data as 64-bit REAL numbers also
preceded by the ANSI/IEEE Standard 488.2-1987 Definite Length Arbitrary
Block header (Figure 3-11). REAL,64 readings are converted by the
digitizer to the actual reading value. Thus, no further conversions are
required.
A line feed (LF) and End-Or-Identify (EOI) follow the last reading in all
formats.
The Definite Length
Arbitrary Block Header
In the definite length arbitrary block header:
• # indicates the data is in an arbitrary block
• < non-zero digit > is a single digit number which shows the number
of digits contained in "digits". For example, if the "digits" value is
100 or 2000, the "non-zero digit" value is 3 or 4, respectively.
• < digits > is the number of 8-bit data bytes which follow the header.
• <8-bit data byte >are the digitizer readings. For the PACKed
format, each reading is two bytes. For the REAL,64 format, each
reading is eight bytes.
Following the last reading in each block is the line feed (LF) character. The
line feed must be read from the buffer to prevent error -410 "Query
INTERRUPTED" occurs the next time data is read from the digitizer.
Packed Reading
Conversions
When the packed reading format is specified with the FORMat command,
or when readings are read from memory and transferred to the VME bus or
Local bus, the readings must be converted from signed, two’s complement
numbers to voltages. Additionally, when FETChing packed readings, the
definite length arbitrary block header must be removed. This section
explains how to separate the block header from the packed data, and how to
convert the data to voltages.
134 Understandin
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the HP E1429 Di
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itizer Chapter 3