8/16 channel mode, Bipolar/unipolar mode, Pacer edge – Measurement Computing CIO-DAS1401/12 User Manual
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CIO-DAS1401/12User's Guide
Installing the CIO-DAS1401/12
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8/16 Channel mode
Use the channel select switch to configure the analog inputs for eight differential or 16 single-ended inputs. Use
the single-ended input mode if you have more than eight, low-noise analog inputs to sample. Using the
differential input mode allows up to 10 volts of common mode noise rejection.
The CIO-DAS1401/12 is shipped with this switch set for 16 single-ended mode(see Figure 4). Set it for the
type (or number) of inputs you require.
8
16 CHAN
Figure 4. 8/16 Channel mode switch
Bipolar/Unipolar mode
Use the Bipolar/Unipolar select switch to select the polarity of the A/D converter.
The CIO-DAS1401/12 is shipped with this switch set for Bipolar (see Figure 5). The switch controls all A/D
channels. You cannot mix bipolar and unipolar channels, however you can measure a unipolar input in the
bipolar mode — for example, you can monitor a 0 to 5V input with a ±5 V channel.
UNI
BIP
Figure 5. Bipolar/Unipolar switch
Input amplifier gain is controlled by a software-programmed register located at Base + B hex (11 decimal).
Refer to the Register Map for the CIO-DAS1400 Series at
for details on this register.
Pacer edge
The original Keithley MetraByte DAS-1600 was designed such that A/D conversion initiated on the falling
(trailing) edge of the convert signal from the internal pacer. Neither the original DAS-16, nor any of the other
DAS-16 derivations convert on the falling edge.
When using the falling edge to start the conversion, the A/D may be falsely triggered by 8254 pacer clock
initialization glitching (easy to avoid but a real possibility in the DAS-1600). Converting on the falling edge
mode also may lead to timing differences if the CIO-DAS1401/12 board is used as a replacement for an older
DAS16 series board.
Because using the falling edge trigger is undesirable, the CIO-DAS1401/12 has a jumper which allows you to
select the internal pacer signal edge used to start the A/D conversion. The jumper has no effect on an external
pacer signal (EXTCLOCK). The falling edge trigger option is provided for compatibility with software for a
DAS-1600 using the AS-1600 drivers, AND, if you observe sample timing differences when using the CIO-
DAS1401/12 with that software.