Latest posts by Reza Mousavi see all.The RS protocol is a popular serial interface that is used to connect computers to peripheral devices such as modems. Set when incoming ring detected - used for auto-answer application.Īuthor Recent Posts. DCE Modem raises when incoming call detected used for auto answer applications. The male connector has the pins sticking out! Only needed if second channel being used. Some manufacturers mark each pin number on the plastic housing at the rear of the connector. Generally Pin 1 is marked on the front of the connector right next to the pin - though you may need a magnifying glass to read it. These diagrams show the male grey background and female black background pin numbering for DB9 and DB25 sub-miniature connectors. This is called a NULL no modem configuration. When PCs are connected back-to-back each end is acting as a DTE there is no DCE in this case and consequently certain signals may have to be looped in the connection to satisfy any input signal requirement. RS defines both the physical and electrical characteristics of the interface.

Epson serial cable pinout db9 to db9