Data Acquisition

110 850300 800600 7001200 5002400 2004800 1009600 7019200 50Table 6.4Demonstrated maximum cable lengths with EIA-232 interface6.2.2 Interface mechanical characteristicsAlthough not specified by RS-232C, the DB-25 connector (25 pin D-type) has become soclosely associated with RS-232 that it is accepted as the de facto standard. On some RS-232compatible equipment, where not all the control lines are required for handshaking, thesmaller DB-9 connector (9 pin D-type) is commonly used.The pins of the DB-9 connector are usually allocated as follows:• Pin 2 – receive data• Pin 3 – transmit data• Pin 7 – signal groundWhile this pin configuration is likely to be adhered to by manufacturers at the computerscommunications interface, it is possible (and often likely) that the data receive and transmitlines on remote stand-alone systems are on different pins of the DB-9 connector. It is thereforewise to consult the manufacturers’ data sheets.The common RS-232 pin assignments for both the DB-9 and DB-25 connectors are shownin Table 6.5, below (continued on the following page).1 Received line signal Shield2 Received data Transmitted data3 Transmitted data Received data4 DTE ready Request to send5 SignalClear to sendcommon/ground6 DCE ready DCE ready7 Request to send Signal ground/common8 Clear to send Received line signal9 Ring indicator + Voltage (testing)10 – Voltage (testing)11 Unassigned12