Kenwood TM-255A Instruction Manual page 12

For CW operation, connect your key or electronic
keyer to the KEY jack on the rear panel. Use a 3.5
mm diameter mono (2-conductor) plug. When using
an electronic keyer, ensure the keyer wiring polarity is
correct.
+5V
io current approximately 1 mA
GND GND +
PACKET EQUIPMENT
If you intend to use this transceiver for Packet
operation, you will need the following equipment:
+ Personal computer with communications software
(Alternatively, a "dumb" terminal capable of
sending ASCII commands)
+ TNC (Terminal Node Controller)
* TNC power supply
« RS-232C cable
* 6-pin mini DIN plug and cable (optional PG-5A)
Refer to the accompanying diagram and the
associated hardware instruction manuals to configure
the equipment as shown. Connect your TNC to the
DATA connector on the transceiver Rear Panel using
a cable equipped with a 6-pin mini DIN plug. You can
use the microphone connector on the Front Panel;
however, the DATA connector is recommended for
the following reasons:
* The DATA connector uses connections at different
modulation/demodulation points depending on the
transmission speed selected via Menu B, No. 77
{page 22}. Therefore, using the DATA connector
will give optimum performance especially if using
9600 bps.
+ Using a mini DIN plug with a good-quality shielded
cable will provide better rejection from computer
noise.
* Easier to switch between voice and data modes.
No cable changes necessary therefore less
chance of damaging the connectors.
Do not share a single power supply between the
transceiver and the TNC. Keep as wide a separation
between the transceiver and computer.as practical to
reduce noise-pickup by the transceiver.