RS 232 stands for Recommended standard number 232. This interface is an age old, and yet it is being used for interconnecting DTE and DCE. It is also one of the maximum used standards for data exchange. The simplicity of configuration and huge capability has rendered this standard a very successful run in the interface field. In our previous post, we discussed about the history of RS 232. In this post, we will focus on various types of RS 232 signals.

        RS 232 SIGNALS - 9     RS 232 SIGNALS - 25

The various Rs 232 signals are:

  •  TD (transmit data) – The TD bus line is used by the DTE system to transmit the desired data to the DCE system. DTE system keeps this line in a marked position when it is in idle (not transmitting) condition.
  • RD (receive data) – This bus line is used by the DTE system to recieve the transmitted data from the DCE system. DCE puts this channel/line in a marked position when it is in idle (not receiving) condition.
  • RTS /CTS (Request To Send/Clear to send) – RTS and CTS lines are in use only if the “hardware flow control” option has been preferred/selected in the DTE and DCE systems.  RTS line is used by the DTE system to tell the other end system that it is ready and capable of receiving data. This is done by putting this line in marked condition. However, in case if the DTE is incapable of receiving data, then this line will be placed in low condition. This will indicate the DCE that the DTE is not incapable of receiving any data and so the data transmission will be stopped by DCE. As soon as the DTE system is prepared of receiving data, it will again put the line to marked condition again. This procedure is also known as handshaking.
  • DTR (Data Terminal Ready) – This line works almost same as RTS.
  • DSR (Data Set Ready) – This line works almost same as CTS. Both the DTR and DSR have been designed initially to provide a secondary mode for handshaking procedure.
  • CD (Carrier Detect) – This line is used to provide an indication to the modem about the detection of a carrier tone or connection of another modem.
  • RI (Ring Indicator) – This line is marked up/low by the DCE to provide the indication of an incoming call.