Model 6485 Picoammeter Instruction Manual DISPlay, FORMat, and SYSTem 13-5
IEEE-754 single precision format
REAL 32 or SREal will select the binary IEEE-754 single precision data format.
Figure 13-1 shows the normal byte order format for each data element. For example, if all
three data elements are selected, the data string for each reading conversion is made up of
three 4-byte data blocks. Note that the data string for each reading conversion is preceded
by a 2-byte header that is the binary equivalent of an ASCII # sign and 0. Figure 16-2 does
not show the byte for the terminator that is attached to the end of each data string. Note
that the byte order of the data string can be sent in reverse order.
Figure 13-2
IEEE-754 single precision data format (32 data bits)
During binary transfers, never un-talk Model 6485 until after the data is read (input) to the
computer. Also, to avoid erratic operation, the readings of the data string (and terminator)
should be acquired in one piece. The header (#0) can be read separately before the rest of
the string.
The number of bytes to be transferred can be calculated as follows:
Bytes = 2 + (Rdgs x 4) + 1
where: 2 is the number of bytes for the header (#0).
Rdgs is the product of the number of selected data elements, arm count and
trigger count.
4 is the number of bytes for each reading.
1 is the byte for the terminator.
For example, assume the instrument is configured to perform 10 measurements and send
them to the computer using the binary format:
Bytes = 2 + (10 x 4) + 1
= 43
Byte 1
70
Header Byte 2
70
Byte 3
70
Byte 4
70
se f
#0
s = sign bit (0 = positive, 1 = negative)
e = exponent bits (8)
f = fraction bits (23)
Normal byte order shown. For swapped byte order,
bytes sent in reverse order: Header, Byte 4, Byte 3
Byte 2, Byte 1.
The header and terminator are sent only once for each READ?.
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