terminations, the data bus signal is
typically 7 Volts P-P at point 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”
signal applied to the “INHIBIT” takes
priority over the condition of the
data inputs and disables the
transmitter (See Transmitter Logic
Waveform,
Figure 1).
The
Transmitter may be safely operated
for an indefinite period with the bus
(point A) short circuited at 100%
duty cycle.
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 Waveform,
Figure 2).
The pre-set internal thresholds
will detect data bus signals, point
A Figure 5, exceeding 1.20 Volts
P-P and reject signals less than
0.6 Volts P-P when used with a
transformer (See Figure 5 for
transformer data and typical
connection).
A low level at the RX Strobe
input inhibits the DATA and
DATA outputs. If unused, a 2K
pull-up to +5 Volts
is
recommended.
Figure 1 — Transmitter Logic Waveforms Idealized
DATA IN
DATA IN
INHIBIT
LINE TO LINE
OUTPUT
Note:
DATA and DATA inputs must be complementary waveforms or 50% duty cycle average, with no delays between them,
and must be in the same state during off times (both high or low).
Figure 2 — Receiver Logic Waveforms Idealized (ACT4489D)
LINE TO LINE
INPUT
STROBE
DATA OUT
DATA OUT
Note overlap
Aeroflex Circuit Technology
2
SCD4489D REV A 1/30/98 Plainview NY (516) 694-6700
AEROFLEX [ AEROFLEX CIRCUIT TECHNOLOGY ]
