Quad Line Driver  (276-2520)  Application Information Faxback Doc. # 14281

The 1488 quad driver and its companion the 1489 quad receiver; provide a
complete interface system between DTL or TTL logic levels and the RS232C
defined levels.  The RS232C requirements as applied to drivers are
discussed.

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

The required driver voltages are defined as between 5 and 15-volts in
magnitude and are positive for a logic "0" and negative for a logic "1". 
These voltages are so defined when the drivers are terminated with a 3000
to 7000-ohm resistor.  The 1488 meets this voltage requirement by
converting a DTL/TTL logic level into RS232C levels with one stage of
inversion.

OTHER APPLICATIONS

The 1488 is an extremely versatile line driver with a myriad of possible
applications.  Several features of the drivers enhance this versatility:

1.  Output Current Limiting- this enables the circuit designer to define
    the output voltage levels independent as power supplies and can be
    accomplished by diode clamping of the output pins. 

2.  Power-Supply Range- as can be seen from the schematic drawing of the
    drivers, (Figure 1) the positive and negative driving elements of the
    device are essentially independent and do not require matching power-
    supplies.  In fact, the positive supply can vary from a minimum seven
    volts (required for driving the negative pulldown section) to the
    maximum specified 15 volts.  The negative supply can vary from
    approximately -2.5 volts to the minimum specified -15 volts.  The 1488
    will drive the output to within 2 volts of the positive or negative
    supplies as long as the current output limits are not exceeded.  The
    combination of the current-limiting and supply-voltage features allow
    a wide combination of possible outputs within the same package.  Thus,
    if only a portion of the four drivers are used for driving RS232C
    lines, the remainder could be used for DTL to MOS or even DTL to DTL
    translation.  Figure 3 shows one such combination.

(TK/all-03/20/95)