Introduction
RS232 - the standard of the asynchronous interface (serial port), was at one time the most popular interface for digital devices for various purposes. In the first computers, his physical presence was mandatory. Even now, the Windows operating system is capable of emulating a number of virtual COMs without having their physical implementations. Some probably remember computer mice, printers, scanners and other peripherals connected to the computer through this port.
Pinout of PC serial port (RS-232 DE9) and layout of 9 pin D-SUB male connector and 10 pin IDC male connector. This RS232C DE-9 (usually miscalled DB-9) port is very common and available at almost any PC, some Sun (at least Ultra 5/ 10, Blade 100/150) and many other computers. Document includes description of how PC serial mouse works. Computer Mouse Interface Bus The serial mouse port is not in common usage. The Mouse port found on most Personal Computers uses a 6-pin mini DIN connector and has the pin out shown the PC Mouse pinout page. All thought not as common as the PS/2 Mouse interface, a mouse may also be found with a serial interface. D3-350 to Serial printer/data terminal using RS-232. Connecting encoders to the D2-CTRINT. D2-250 to D2-250 RS-485 with a FA-ISONET. D2-DSCBL-2 pinout for using remote I/O on a D2-250, D2-250-1, or D2-260 PLC. FA-ISOCON to PC wiring diagram. DL-250 Port 2 Cable (D2-DSCBL-2) D4-IOCBL-1 Cable Color Codes. PS/2 connector is developed by IBM for connecting mouse and keyboard. It was introduced.
Now the situation has changed, the computer peripherals are connected to the PC using faster USB ports. But in instrumentation, RS232 takes the rightful place, it is rare to see a digital device that can be configured by a computer without this interface. Quite often RS232 port serves as a transition link to the RS485 interface, connected via a miniature adapter.
Db9 Serial Port
The information in RS232 is transmitted in duplex mode
- Logical «0» - positive voltage from +5 to +15 V
- Logical «1» - negative voltage from -5 to -15 V
Due to the design features, the length of the communication line is small, usually no more than 10 meters.
Initially, the interface RS232 connector was designed as a 25-pin connector. In this DB25 connector, a secondary RS232 serial channel was also provided. But in practice, only one channel was realized. Computers in which both channels were presented were very rare, for example Sun SparcStation 10/20 and Dec Alpha Multia. Also on some modems there was a secondary channel, it signaled the status of the modem, while the primary one was busy with data transmission. In our time, the more 9-pin DB9 version of RS232 has taken root.
Pinout of the RS232 connector
25-pin (DB25) RS232 connector
On the diagram of the 25-pin RS232 connector, the black color indicates the pins common to both types of connectors. The figure and the table below show how to connect the adapter from the 25-pin connector to the 9-pin connector.
Adapter cable from 25 pin RS232 to 9 pin
| DB9 | DB25 | Description |
| 1 | 8 | Data carrier detect |
| 2 | 3 | Receive data |
| 3 | 2 | Transmit data |
| 4 | 20 | Data terminal ready |
| 5 | 7 | Signal ground |
| 6 | 6 | Data set ready |
| 7 | 4 | Request to send |
| 8 | 5 | Clear to send |
| 9 | 22 | Ring indicator |
Plug for RS232
Below is the RS232 connector pinout for testing computer serial port. Data and handshake lines connected. In this case, the sent data is immediately returned back and analyzed by the standard serial port verification software.
| DB9 | DB25 | Description |
| 1 + 4 + 6 | 6 + 8 + 20 | DTR -> CD + DSR |
| 2 + 3 | 2 + 3 | Tx -> Rx |
| 7 + 8 | 4 + 5 | RTS -> CTS |
Null-modem cables for RS232
Pc Serial Pinout
The simplest way to connect two computers together is to use a null modem RS232 cable. For a simple solution, a three-wire RS232 scheme is sufficient, where one wire is the signal ground, the second is the receiver, and the third is the transmitter. But depending on the type of software, some kind of handshake may be required. Below are the most popular types of null modem cables for RS232.
Simple null-modem cable without handshaking
This simple pinout of the cable does not allow monitoring of data transmission and reception at the «hardware level», but at the software level, monitoring is possible using XOFF analysis and XON symbols. Not all programs are able to work with such a cable. This is more a theoretical concept. There are also cables with a handshaking simulation on a «stub» and partial handshaking without the ability to control the data transmission at the «hardware level». The following is the RS232 cable wiring with full handshaking recommended by Microsoft.
RS232 null modem cable with full handshaking
Pc Com Port Pinout
Here, seven wires are used, and this RS232 pinout has become essentially standard.