Quad Line Receiver  (276-2521)        Application     Faxback Doc. # 14284
                                      Information

The 1489 quad receiver and its companion circuit, the 1489 quad driver,
provide a complete interface system between DTL or TTL logic levels and
the RS-232C defined levels.  The RS-232C requirements as applied to
receivers are discussed herein.

Useful for interfacing peripheral devices (such as modems, ham radio
terminal units, auxiliary keyboards, controller or controlling units,
sound synthesizers, etc.) to microcomputers and data terminals.  Also
suitable for mixing logic families within the same circuit.

The required input impedance is defined as between 3000 ohms and 7000 ohms
for input voltages between 3.0 and 25 volts in magnitude; and any voltage
on the receiver input in an open circuit condition must be less than 2.0
volts in magnitude.  The 1489 circuit meets these requirements with a
maximum open circuit voltage of one v BE.

The receiver will detect a voltage between -3.9 and -25 volts as a logic
"1" and inputs between +3.0 and +25 volts as a logic "0".  On some
interchange leads, an open circuit or power "OFF" condition (300 ohms or
more to ground) shall be decoded as an "OFF" condition or logic "1".  For
this reason. the input hysteresis threshold of the 1489 circuit is above
ground.  Thus, an open or ground input will cause the same output as a
negative or logic "1" input.

A separate response control terminal is provided for each receiver.  A
resistor or resistor and bias voltage source may be connected between this
terminal and ground to shift the input threshold voltage levels.  An
external capacitor (typically 0.1 MFD) may be connected between this
terminal and ground to provide input noise filtering.

(TK/all-03/20/95)