Introduction

The TCC-80/80I media converters provide complete
signal conversion between RS-232 and RS-422/485, without requiring
an external power source. The converters support both half-duplex
2-wire RS-485 and full-duplex 4-wire RS-422/485, either of which can
be converted between RS-232’s TxD and RxD lines.

Automatic data direction control
is provided for RS-485. In this case, 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.

Port Power over RS-232

The RS-232 port of the TCC-80/80I is a DB9 female socket that can connect directly to the host PC, with power drawn from the TxD line. Regardless of whether the signal is high or low, the TCC-80/80I can obtain enough power from the data line. However, external power can be used if the handshake line is not available, if the serial cable is too long, or if the RS-232 device is a low-power device. For external power, a five to twelve VDC power supply can be connected using an adapter or a USB power cord.

Port Power Dissipation

When installing a TCC-80 or TCC-80I converter, it is important to pay attention to power consumption, RS-232 cable length, and RS-422/485 transmission distance. In general, the TCC-80 and TCC-80I obtain 50 mW of power from the power source. Standard PC COM ports can provide 70 to 90 mW of power if the TxD, RTS, and DTR lines are connected. Moreover, the RS-232 cable should be shorter than 15 m (@ 9600 bps) to ensure that less power is lost from the host/device to the TCC-80. The remainder of the supplied power is used for transmitting the RS-422/485 signal.

Port Power and Optical Isolation

The RS-232 port of the TCC-80/80I is a DB9 female socket that can connect directly to the host PC, with power drawn from the TxD line. Electrical 2.5 kV isolation for the TCC-80I is achieved with a photo coupler that transforms the electrical signal into light, and then re-transforms the light back into an electrical signal on the other side. In this way, the two electrical circuits are completely isolated from each other. This also protects the devices from ground loop currents, reduces damage caused by data loss, and prevents damage to the communication interfaces.

LED Port Power Indicator

It’s easy enough to test
the serial device with a multimeter to determine that the serial device
will provide enough power to the media converter. However, it’s even
easier to let the TCC-80I test the device for you. Simply connect
the TCC-80I to the device’s RS-232 port and set the SW4 switch to
Test mode. If the port power LED indicator lights up, the TCC-80I
is receiving enough power. If the LED does not light up, you will
need to attach an external power source to the TCC-80I.