If you have been in computers for a while then you will know that selecting the right RS232 serial cable can be a problem. Below you will find some information on the most common serial RS232 cables in normal computer use. You can find the pinouts for the RS232 cable listed below as well as other information on the RS232 driver. Some would like to use a USB cable on it. Search this website for more information.
How do I connect devices and computers using RS232?
Note the difference between the RS232 DB9 and also the DB25 pin layouts as there is another page where it is described as to how to connect the two serial connectors on your equipment. The pinout below will also show you the DEC modified modular jack which was designed and built by Digital Equipment Corporation. The difference being that the interface is differential it is possible to connect RS232 compatible devices with this type of interface mainly because the voltage levels of the bit streams are in the same range.
Note that these two can be connected with a converter. The “Data carrier detect” is Pin 1 (DB9) and Pin 8 (DB25). You can see these on the two diagrams. There is also the “Receive data” is Pin 2 (DB9) and Pin 3 (DB25) and the “Transmit data” is Pin 3 (DB9) and Pin 2 (DB25). There is also the “Data terminal ready” which is Pin 4 (DB9) and Pin 20 (DB25) as well as “Signal Ground” which is Pin 5 (DB9) and Pin 7 (DB25). There is also the “Data set ready” which is Pin 6 (DB9) and Pin 6 (DB25). Also the “Request to send” where there is Pin 7 (DB9) and Pin 4 (DB25) as well as “Clear to send” which is Pin 8 (DB9) and Pin 5 (DB25) and the final being the “Ring indicator” which is Pin 9 (DB9) and Pin 22 (DB25). This would be converting a DB9 to a DB25 serial connector.
How to install and setup RS 232 on Ubuntu FT232R USB UART