Keithley KUSB-3100, User Manual

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Chapter 2
14
Data Transfer
Before you begin acquiring data, you must allocate buffers to hold
the data. During acquisition, a Buffer Done message is returned
whenever a buffer is filled. This allows you to move and/or process
the data as needed.
It is recommended that you allocate a minimum of three buffers for
analog input operations, specifying one of the following buffer wrap
modes in software:
• None – Data is written to multiple allocated input buffers
continuously; when no more empty buffers are available, the
operation stops. This wrap mode guarantees gap-free data.
• Multiple – Data is written to multiple allocated input buffers
continuously; if no more empty buffers are available, the module
overwrites the data in the current buffer, starting with the first
location in the buffer. This process continues indefinitely until
you stop it. This mode does not guarantee gap-free data.
Data Format
The KUSB-3100 module uses twos complement encoding to represent
bipolar input ranges. In software, the analog input value is returned
as a code.
To convert a twos complement code into a voltage, use the following
formulas:
LSB = FSR = 20 V = 0.0048828 V
2
N
4096
Code
Offset Binary
= Code
Twos Complement
XOR 2
N-1