Digital Output Devices
For an application running on your PC to control your transceiver or antenna switch, physical connections are required. The are typically accomplished using any of three digital output devices commonly found on PCs:
a serial port's data output signal (TxD)
a serial port's modem control output signals (DTR or RTS)
- a parallel port's data and control signals
Serial port data output and modem control output signals employ RS-232 voltage levels (+12 VDC, -12 VDC). Since in many cases the transceiver or antenna switch inputs being controlled require TTL voltage levels (+5 VDC, 0 VDC), a level converter may be needed.
Parallel port data and control outputs employ TTL voltage levels.
Both serial and parallel ports are available on printed circuit cards that plug into a PC motherboard, and on adaptors that plug into USB ports.
If necessary, you can change the COM port number that Windows assigns to a USB-to-serial-port adaptor.