Data Acquisition

13 Sec clear to send14 Sec transmitted data15 Transmitter signal DCE elementtiming16 Sec received data17 Receiver signal DCE element timing18 Local loopback19 Sec request to send20 DTE ready21 Remote loopback/signal qualitydetector22 Ring indicator23 Data signal rate24 Transmit signal DTE element timing25 Test modeTable 6.5Table of the common DB-9 and DB-25 pin assignments for EIA-232 6.2.3 Functional description of interchange circuitsThe EIA circuit functions are defined, with reference to the DTE, as follows:• Pin 1: Protective ground (shield)A connection is seldom made between the protective ground pins at each end.Their purpose is to prevent hazardous voltages, by ensuring that the DTE andDCE chassis are at the same potential at both ends. However, there is a dangerthat a path could be established for circulating earth currents, so, usually the cableshield is connected at one end only.• Pin 2: Transmitted data (TXD)This line carries serial data from pin 2 on the DTE to pin 2 on the DCE. The lineis held at MARK (or a negative voltage) during periods of line idle• Pin 3: Received data (RXD)This line carries serial data from pin 3 on the DCE to pin 3 on the DTE.• Pin 4: Request to send (RTS)The RTS line is a request to send from the DTE to the DCE. This line is used inconjunction with the CTS line to do hardware control. The DCE will not enablethe CTS line until the DTE enables its RTS line.• Pin 5: Clear to send (CTS)When a half-duplex modem is receiving, the DTE keeps RTS inhibited. When itbecomes the DTE’s turn to transmit, it advises the modem by asserting the RTSpin. When the modem asserts the CTS, it informs the DTE that it is now safe tosend data.• Pin 6: Data set ready (DSR)This is also called DCE ready. In the answer mode, the answer tone and the dataset ready are asserted two seconds after the telephone goes off hook.