IBM Series 1 User Manual page 141

is used, some external non-IBM supplied power source must be
used to generate current for the receive current loop.
The equivalent circuit for the isolated contact sense inputs
is a series resistance between the input pins.
Non-I..§ol2:te~ Contact Sense. Two connecto[' pins are
available
for
the signal input. These inputs are used when
it is desired that the teletypewriter adapter card generate
current for the receive current loop.
The equivalent circuit
for the non-isolated contact
sense inputs is a ['esistor in series with a voltage source.
lIb.
One
connector pin is available for
TTL
level input.
The TTL input is non-isolated.
ETA. One pin is available for ETA RS232-C level input. This
input is non-isolated.
Gr.Qundi.n.g.
The
cable shield ground wire must
be
connected
to fr~ gro~Q at the point of entry into the IBM
enclosure. The cable shielded-ground wire must be connected
to ira.!!~ ground at the user's device end of the cable.
The performance of this interface may be affected by
noise. Appropriate arc suppression, noise filtering, etc.
may be necessary on customer inputs.
Contact sense inputs are isolated from card ground.
TTL and EIA signal ground is tied to logic ground in the
teletypewriter adapter card.
4-18 GA34-0033
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