RS232 pinout RS232 pinout standards exist for both DB9 and DB25 connectors as shown below: DB25 SIGNAL DB9 DEFINITION 1.
Is a standard introduced in 1960 for serial communication transmission of data. It formally defines the signals connecting between a DTE (data terminal equipment) such as a computer terminal, and a DCE (data communication equipment), such as a modem.
The RS-232 standard had been commonly used in computer serial ports. The standard defines the electrical characteristics and timing of signals, the meaning of signals, and the physical size and pinout of connectors. PC serial port is based on RS-232 standard, you may find signals details in the., when compared to later interfaces such as, and, has lower transmission speed, short maximum cable length, large voltage swing, large standard connectors, no multipoint capability and limited multidrop capability. In modern personal computers, has displaced RS-232 from most of its peripheral interface roles. Many computers no longer come equipped with RS-232 ports (although some motherboards come equipped with a ) and must use either an external or an internal expansion card with one or more serial ports to connect to RS-232 peripherals. Nevertheless, thanks to their simplicity and past ubiquity, RS-232 interfaces are still used — particularly in industrial machines, networking equipment, and scientific instruments where a short-range, point-to-point, low-speed wired data connection is adequate. This PC serial port interface is single ended (interconnect two devices only, via ), the data rate is less than 20 kbps. RS232 is the voltage loop serial interface with full-duplex communication represented by voltage levels with respect to system ground.
A common ground between the PC and the associated device is necessary. Hot-plug isn't supported, but sometimes allowed. Nowdays only 9-pin connector is still in use for PCs. DE-9 Pin Signal Name Dir Description 1 DCD Data Carrier Detect 2 RXD Receive Data 3 TXD Transmit Data 4 DTR Data Terminal Ready 5 0V/COM 0V or System Ground 6 DSR Data Set Ready 7 RTS Request to Send 8 CTS Clear to Send 9 RI Ring Indicator Note: Direction is DTE (Computer) relative DCE (Modem) Standard RS232 data packet RS232 data is usually sent as a packet with 7 or 8 bit words, start, stop, parity bits (may be varied). Sample transmission shown on picture: Start bit (active low, usually between +3v and +15v) followed by data bits, parity bit (depends on protocol used) and finished by stop bit (used to bring logic high, usually between -3v and -15v). Sample RS232 serial port device. How serial mouse works Typical PC mouse controlling system has the following parts: sensors - mouse controller - communication link - data interface - driver - software.
Sensors are the movement detectors which sense the mouse movement and button swiches which sense the button states. Mouse controller reads the state of those sensors and takes acount of current mouse position. When this information changes the mouse controller sends a packet of data to the computer serial data interface controller. The mouse driver in the computer received that data packet and decodes the information from it and does actions based on the information.
PC RS232 serial mouse voltage levels: Mouse takes standard RS-232C output signals (+-12V) as its input signals. Those outputs are in +12V when mouse is operated. Mouse takes some current from each of the RS-232C port output lines it is connected (about 10mA). Mouse send data to computer in levels that RS-232C receiver chip in the computer can uderstand as RS-232C input levels.
Mouse outputs are normally something like +-5V, 0.5V or sometimes +-12V. Mouse electronics normally use +5V voltage. Serial device hardware implementation PC serial mouse uses typically DTR and RTS lines for generating +5V power for microcontroller circuit in the mouse. Because typical optomechanical mouse also needs power for 4 leds in the optocoupler movevement detectors, there is not much power to loose.
A typical approach is to use diodes to take current from DTR and RTS lines and then feed it through resistor to all of the (infrared) leds in the movement detectors. The positive power supply usually taken from RTS and DTR lines (just after the diodes and before the resistor going to leds).
The negative supply for transmitter is taken from TD pin. Typical PC serial port mouse takes 10 mA total current and operates at voltage range of 6-15V.