HI-8482
FUNCTIONAL DESCRIPTION
The HI-8482 contains two independent ARINC 429 receive
channels. The diagram in Figure 1 illustrates a typical HI-
8482 receive channel.
The differential ARINC signal input is converted to a positive
signal referenced to ground through level shifters and a
unity gain differential amplifier.
A positive differential input signal is converted to a positive
signal on the plus output of the differential amplifier. This
output is proportional in amplitude to the original input
signal. At the same time, the corresponding MINUS output
is pulled to GND. Likewise when a negative input signal is
present at the ARINC inputs, a positive signal is present on
the MINUS output and the PLUS output is pulled to GND.
The outputs of the differential amplifier are compared with
the ONE, ZERO and NULL threshold levels to produce the
appropriate logic level on the OUTA and OUTB outputs of
the device. The ARINC clock signal may be recovered
through a NOR function of OUTA and OUTB.
The test inputs logically disconnect the outputs of the
comparators from OUTA and OUTB and force the device
outputs to one of the three valid states (Figure 5). This
alleviates having to ground the ARINC inputs during test
mode operation.
ARINC LEVELS
The ARINC 429 specification requires the following
detection levels:
STATE
ONE
NULL
ZERO
DIFFERENTIAL VOLTAGE
+6.5V to +13V
+2.5V to -2.5V
-6.5V to -13V
The HI-8482 guarantees recognition of these levels with a
common mode voltage with respect to GND less than
±5V for the worst case condition.
NOISE
The input hysteresis is set to reject voltage level transitions
in the undefined region between the maximum ZERO level
and the minimum NULL level and the undefined region
between the maximum NULL level and the minimum ONE
level. Therefore, once a valid input differential voltage
threshold is detected, the outputs will remain at a valid logic
state until a new valid input voltage is detected.
In addition to the hysteresis, the CapA and CapB pinsmake
it possible to add simple RC filters to the ARINC inputs.
TESTA
TESTB
INA
CAPA
INB
CAPB
LEVEL
SHIFT
DIFF
AMP
LEVEL
SHIFT
Detect
Level
Comp
Comparators
w / hysteresis
Comp
Detect
Level
HOLT INTEGRATED CIRCUITS
2
HOLTIC [ HOLT INTEGRATED CIRCUITS ]
