1:1 transformer, isolated on the data
bus side with two 52.5 Ohm fault
isolation resistors, and loaded by
two 70 Ohm terminations plus
additional receivers, the data bus
signal produced is 7.0 Volts
minimum P-P at A-A’. (See
Figure 5.) When both DATA and
DATA inputs are held low or high, the
transmitter output becomes a high
impedance and is “removed” from
the line. In addition, an overriding
“INHIBIT" input provides for the
removal of the transmitter output
from the line. A logic “1” applied to
the “INHIBIT” takes priority over the
condition of the data inputs and
disables the transmitter. (See
Transmitter
Logic
Waveforms,
Figure 1.)
The transmitter utilizes an active
filter to suppress harmonics above
1 MHz to meet Macair specifications
A-3818, A-4905, A-5232 and
A-5690. The transmitter may be
safely operated for an indefinite
period at 100% duty cycle into a
data bus short circuit.
Receiver
The Receiver section accepts
bi-phase differential data at the input
and produces two TTL signals at the
output. The outputs are DATA and
DATA, and represent positive and
negative excursions of the input
beyond a pre-determined threshold.
(See Receiver Logic Waveforms,
Figure 2.)
The internal threshold is nominally
set to detect data bus signals
exceeding 1.05 Volts P-P and
reject signals less than 0.6 Volts
P-P when used with a 1:1 turns
ratio transformer. (See Figure 5 for
transformer data and typical
connection.) This threshold setting
can be held by grounding the
appropriate pins or modified with
the use of external resistors.
A low level at the Strobe input
inhibits the DATA and DATA
outputs. If unused, a 2K Ohm
pull-up
to
+5
Volts
is
recommended.
Figure 1 - Transmitter Logic Waveforms
DATA IN
DATA IN
INHIBIT
LINE TO LINE
OUTPUT
Notes: 1. Line to line waveforms illustrate Macair signals, MIL-STD-1553 signals are trapezoidal
2. DATA and DATA inputs must be complementary waveforms or 50% duty cycle average, with no delays between them.
3. DATA and DATA must be in the same state during off time (both high or low).
Figure 2 - Receiver Logic Waveforms
LINE TO LINE
INPUT
DATA OUT
DATA OUT
Note overlap
NOTE
:
Waveforms shown are for normally low devices. For normally high receiver output
level devices, the receiver outputs are swapped as shown by the dashed lines
Aeroflex Circuit Technology
2
SCD4404 REV D 10/27/99 Plainview NY (516) 694-6700
AEROFLEX [ AEROFLEX CIRCUIT TECHNOLOGY ]
