In RIS, the 9400A digitizes 24000 data points (except: 24800 at I ~sec-
/div and 25000 at 2 Bsec/div; see Section 5.1.2). In this mode and in
SEQNCE mode, it may happen that the memory is slightly too small to
cover the entire screen. In this case, the waveform does not extend all
the way to the left hand side of the display screen, and the address of
the first valid data point of the record is a positive number. The
principle is still maintained, that address 0 corresponds to the data
point at the left edge of the screen, even if it refers to a virtual
data point. This case occurs in interleaved sampling at 0.5 usec/div:
left edge
. 5~$/di~ interleaved
of screen
0
~000
25O00
digltizeda displayed record, 24000pts, 4.8ps
m
~ssing dqta on displo
As the data-record limits depend on the time base and on the acquisi-
tion mode, the 9400A allows the user to read these address limits with
the command "INSPECT xx. LIHIT". The response is a data block of 2
16-bit words, corresponding to the lowest and the highest address o£
the data record in question. If the user specifies larger limits than
valid, the 9400A automatically replaces them with the legal ones (and
sets the VALUE ADAPTED bit in the Main Status Byte STB 1).
7.10 Interpretation of Waveform Data Values
The conversion of the integer waveform data into volts requires the use
of three scale and offset parameters found in the descriptor (see
Section 7.7):
- Fixed gain, transmitted as an 8-bit BYTE at address 0 relative
to the beginning of the descriptor. This coded value can be
transformed into a number of VOLTS/DIV with a user-defined
table. This transformed value is called ’gain’ in the formula.
- Variable gain, transmitted as an 8-bit BYTE at address 1
relative to the beginning of the descriptor. This value is
called ’vgain’ in the formula below.
- Offset, transmitted as a 16-bit (signed) WORD at address
relative to the beginning of the descriptor. This value is
called ’offset’ in the formula below.
7.10.1
Waveform Data in 8-bit Format
This is the default format of all data records (if the Waveform
Processing option is installed, it is possible to modify it to 16 bits
with the command COMM FORMAT). The unsigned 8-bit "data" values in the
numerical range 0 .... 255 are transformed to volts as follows:
7-50
Remote Operations
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