This RS-232 to RS-422 converter converts unbalanced RS-232 signals to balanced RS-422 signals. The power used for this converter is derived from the transmit data line (pin 2) and the handshake control lines (pins 4, 5, 6, 8, and 20). The converter can derive power from these lines when they are in the positive or negative voltage state. This permits the converter to be used in applications without any regard to software control of the handshake lines. If no handshake lines are available and all power must be derived from the transmit data line, the converter can drive limited cable lengths. A guide for this condition would be to drive only several hundred feet of transmission line and not to terminate the transmission line with a resistor of less than 1000 ohms. When more handshake lines are available longer lengths of cable can be driven. This converter has been tested at 115.2k baud with 4000 feet of cable. For applications where handshake lines are not available and long cable runs are involved, an external power supply can be connected to the male connector on the RS-422 side of the converter on pins 12 (Gnd) and 25 (+12).
