Astronics OMNIBUS II NI PXIe, User Manual

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MODULE CONFIGURATIONS
OmniBus II NI PXIe User Manual 6-3
Family. The configuration value, configval, now allows for setting a high and a
low range. The lower 12 bits of dacval represent the transmit amplitude. The OB2
has a resolution of 8 bits, so the least significant 4 bits are don’t cares. The full-
scale value of FF0h is the default setting.
configval
Constant Description
PARAMCFG1553_DEFAULT Select all default settings ( bold below)
PARAMCFG1553_AMPLON
Enables parametric amplitude control
PARAMCFG1553_AMPLHI
Enables parametric amplitude control high range
PARAMCFG1553_AMPLLO Enables parametric amplitude control low range
PARAMCFG1553_AMPLOFF Disables parametric amplitude control
Table 6.4—MIL-STD-1553 ParamAmplitudeConfig Configval
Constant Range* Output Drive*
PARAMCFG1553_AMPLHI 0V-26V .101*( dacval >> 4)
PARAMCFG1553_AMPLLO 0V-4.9V .019*( dacval >> 4)
Table 6.5—MIL-STD-1553 ParamAmplitudeConfig Output Drive
*Since the actual amplitude and linearity depend on both the line driver and
load, the user must calibrate with the conditions in use for the degree of
accuracy desired. Some line drivers are not capable of putting out very low
voltages; be sure to verify the output under your operating conditions.
6.2.4 Zero-Crossing Distortion
On level P channels, a zero crossing of the transmitted signal can be shifted from
its normal position under software control. This feature allows a specific zero-
crossing to be shifted up to +/- 250 ns, in increments of 5 ns. A zero-crossing shift
can be generated on the leading or mid-bit zero crossing of a specified bit position
in a specified word.
Note: If a zero crossing is delayed, such that the subsequent zero crossing
occurs less than 400 ns later, the timing of the subsequent zero crossing may
also be distorted.