Quatech Freedom USB Adapter User’s Manual Making external connectionsMaking external connectionsRS-232 serial connectionsThe Freedom USB-100 RS-232 adapters all come with standard maleDB-9 connectors. The figure below shows the pin designations.Figure 37 - RS-232 DB-9 pin designationsRS-232-C devices are classified by their function as either DataTerminal Equipment (DTE) or Data Communication Equipment(DCE).Figure 38 - Use of DTEs and DCEs in a communication linkFigure 38 illustrates role ofDTE and DCE devices in acommunications link.Freedom USB-100 adapters are DTE devices that conect to peripheralequipment through a male DB-9 connector. The following table liststhe serial port connector definitions.Table 3 - RS-232 DB-9 signal definitionsDTEconnectionRS-232 signaldescription DB-9Data Carrier Detect (DCD) 1Receive Data (RxD) 2Transmit Data (TxD) 3Data Terminal Ready (DTR) 4Signal Ground 5Data Set Ready (DSR) 6Request To Send (RTS) 7Clear To Send (CTS) 8Ring Indicate (RI) 9DTE- and DCE-type devices have complementary pinouts that allowterminals and modems to connect directly using a one-to-one cable asshown in Figure 39.Rev 2.02 (2/24/2004) Page 29Note: In many applications,DCEs are unnecessary. Thisallows you to use a null modemcable (modem eliminator cable)to directly connect two DTE-type devices.Note: A DTE devices is thecommunication source. A DCEdevice provides a communicationchannel between two DTE-typedevices.
