Making external connections Quatech Freedom USB Adapter User’s ManualSee Figure 39 on the following page for a typical null modem cable.Figure 39 - Cabling requirements for RS-232C devicesRS-422/485 serial connectionsThe Freedom USB-200/300 RS-422/485 adapters all come with standardfemale DB-9 connectors. The figure below shows the pin designations.Figure 40 - RS-422/485 DB-9 pin designationsFreedom USB-200/300 serial USB adapters provide four differentialcommunication signals (either RS-422 or RS-485) per channel.Transmit Data (TxD) and Auxiliary Output (AuxOut) are the twooutput signals. Receive Data (RxD) and Auxiliary Input (AuxIn) arethe two input signals. The adapters also provide a ground signal.The AuxOut pair can carry the UART’s RTS signal. The AuxIn paircan carry the UART’s CTS signal. Alternatively, the AuxOut pair canbe configured to internally loopback to the AuxIn pair, with theUART’s RTS signal also looped back to its CTS signal. The followingtable shows the RS-422/485 connector definitions.Table 4 - RS-422/485 DB-9 signal definitionsAll portsRS-422/485 signal description DB-9Auxiliary Output (AuxOut+) 1Transmit Data (TxD+) 2Signal Ground 3Receive Data (RxD+) 4Auxiliary Input (AuxIn+) 5Auxiliary Output (AuxOut–) 6Transmit Data (TxD–) 7Receive Data (RxD–) 8Note: Refer to AdvancedOptions using Device Managerfor details on software-selectable advanced options.Figure 39 illustrates the RS-232C pinouts for typical DTE-to-DCE and DTE-to-DTE (nullmodem) cables with 25-pinconnectors.Page 30 Rev 2.02 (2/24/2004)
