Regrading RS232 connector was normally user or developper to use 9 pins.about this DB9 connector pinout provisions has done for a secondary serial RS232(Comm port) communication .
For the Definition adn detail of RS232 serial port, including the location pin. What is called a view from below.
In struction, only one serial communication way with accompanying handshaking is present.the very few computers have been factory where both serial RS232 channels are implemented.
Such as of the informations are the Sun SparcStation 10 and 20 models and the Dec Alpha Multia and on a number of Telebit modem models the secondary channel is present too.
It can be used to query the modem status while the modem is on-line and busy communicating. On personal computers, the smaller DB9 version is more commonly used today. The diagrams show the signals common to both connector types in black. The defined pins only present on the larger connector are shown in red. Note, that the protective ground is assigned to a pin at the large connector where the connector outside is used for that purpose with the DB9 connector version.