The Definite Length Arbitrary Block Header

Packed Reading Conversions

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.

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.

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 Understanding the HP E1429 Digitizer

Chapter 3

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HP E1429A manual Packed Reading Conversions, Definite Length Arbitrary Block Header