Aeroflex Circuit Technology

SCD4489D REV A 1/30/98 Plainview NY (516) 694-6700

2

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.

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 1 — Transmitter Logic Waveforms Idealized

Figure 2 — Receiver Logic Waveforms Idealized (ACT4489D)

Note overlap

LINE TO LINE

INPUT

DATA OUT

DATA OUT

STROBE