Keithley DAS-1700 Series
Using the DAS-1700 Series with DriverLINX
•
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The KPCI-1800 Series performs direct memory access (DMA) using the PCI bus
mastering mode. To maintain the high efficiency that bus mastering provides, the
hardware transfers samples in pairs (four bytes at a time) to memory on 4-byte
boundaries. This feature has the following consequences:
•
Each buffer must have an even number of samples (a multiple of four
bytes). If an application requests a DMA-mode task with an odd
number of samples per buffer, DriverLINX returns an "Invalid # of
conversions" error.
•
A sample taken on an odd-numbered clock pulse is not available until
the next even-numbered clock pulse. At high sample rates with
continuous internal or external clocking, this effect is imperceptible. At
very low sample rates, you may observe applications taking twice as
long as expected to acquire a sample. With an external clock that
produces an odd number of pulses and then stops, the application will
not receive the last sample.
Applications that require an odd number of samples per buffer or use an external
clock with an odd, finite number of clock pulses should use interrupt mode instead of
DMA mode. For existing applications that use DMA mode but do not meet these
requirements, the user can cause DriverLINX to substitute interrupt mode for DMA
mode by disabling bus mastering in the KPCI-1800’s Configure DriverLINX Device
dialog.
Analog Input Data Coding
DAS-1700 Series models return Analog Input hardware codes using binary integers
for unipolar ranges and offset binary for bipolar ranges. DriverLINX refers to these
coding schemes as the “native” format.
For any programmable gain, the DAS-1700 models return hardware codes with the
ranges in the following table:
Analog Input
Resolution
Polarity
Analog Input
Hardware Code
12 bits
Unipolar
0 to 4095
12 bits
Bipolar
-2048 to 2047
(right-justified without
sign extension)
*
16 bits (HR models)
Unipolar
0 to 65535
16 bits (HR models)
Bipolar
-32768 to 32767
Native Analog Input hardware codes for each DAS-1700 Series polarity.
*
The KPCI-1800 Series hardware codes are left justified. For compatibility convert to a standard data
type with DriverLINX conversion functions.
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