TCC-80, which is powered
via the RS-232 ports, provides complete signal
conversion between RS-232 and RS-422/485. TCC-80
converts back and forth between RS-232's TxD and
RxD lines and either half duplex 2-wire RS-485
or the balanced signal of full duplex 4-wire RS-422/485.
In addition, TCC-80's outputs have comprehensive
protection against current overload with built-in
15 KV ESD surge protection. TCC-80 is also designed
to provide RS-485 auto data direction control
in which the RS-485 driver is enabled automatically
when the circuitry senses the TxD output from
the RS-232 signal. This means that no programming
effort is required to control the transmission
direction of the RS-485 signal.
RS-232 SerialPort Power
 The
RS-232 port of TCC-80 is designed with a female
DB9 socket to connect directly to the host PC,
with power drawn from the TxD, RTS, and DTR
lines.
Regardless of whether the signal is high or low,
TCC-80 is still able to obtain enough power
from
the combined force of these three data/handshake
lines. For those applications that do not use
the handshake lines, a DC jack is provided for
connecting a 5 to 12 VDC power supply via a
USB
power cord or external power adaptor.
Optional External Power
Termination is thought to be a critical
requirement for port-power devices such as TCC-80.
In most circumstances, termination resistors
are used when the RS-422/485 cable length is
longer
than 100 m. Regardless of how much the data signal
is dissipated, the termination resistors absorb
more than 75 mW of power from the power source
when TCC-80 is unable to use the limited serial
power. In other words, if
long distance RS-422/485 transmission or termination
is required, and no handshake lines are available,
then an external USB power cord or DC power
supply
should be used.
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Port Power Dissipation
When installing an RS-232 port-powered
TCC-80 converter, it is important to pay attention
to the power consumption, RS- 232 cable length,
and the RS-422/485 transmission distance. In general,
TCC-80 itself derives 50 mW from the power source;
a standard COM port on a host PC can provide 70
to 90 mW of power if the TxD, RTS, and DTR lines
are connected. Moreover, the RS-232 cable length
should be shorter than 15 m @ 9600 baudrate to
ensure that less power is lost from the host/device
to the TCC-80. In the end, the rest of the supplied
power is used for transmitting the RS-422/485
signal.
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