A symmetrical pin layout allows to connect two DTE, data terminal ()) directly without using a modem or other DCE data communication equipment.


The original wiring RS232

RS232

For a serial line information arrive at regular intervals (synchronous) or at random intervals (asynchronous). Between a transmitter (DTE) and a receiver (DCE) wiring is right. RS232 cables can be connected in series.
In configurations where 2 DTE are directly connected, a cable of cross linking or \Null-Modem\ should be used. This cable has female connectors at each end.

was developed for 25 pins.
The vast majority of applications RS232

RS232

For a serial line information arrive at regular intervals (synchronous) or at random intervals (asynchronous). Between a transmitter (DTE) and a receiver (DCE) wiring is right. RS232 cables can be connected in series.
In configurations where 2 DTE are directly connected, a cable of cross linking or \Null-Modem\ should be used. This cable has female connectors at each end.

use only 3 links : TX, RX and GND.

9 pins RS232

RS232

For a serial line information arrive at regular intervals (synchronous) or at random intervals (asynchronous). Between a transmitter (DTE) and a receiver (DCE) wiring is right. RS232 cables can be connected in series.
In configurations where 2 DTE are directly connected, a cable of cross linking or \Null-Modem\ should be used. This cable has female connectors at each end.

connectors are commonly used.
In mixed applications, a 9-to-25 converter can be used to plug in different sizes.
Two other contacts of signal, RTS and CD are sometimes used when interfacing to modems or RJ11

RJ11

RJ11 – Regitered Jack 11 – is used for the landline. It is an international standard for connecting the fixed telephone to the telecommunications network.
RJ11 uses a 6-slot connector. In this one RJ11 has 6 slots (positions) and two drivers, the standard is written 6P2C. The information transmitted on the line can be digital (DSL) or analog. The telephone cable that arrives at the subscriber has 4 conductors

.

Full RS232

RS232

For a serial line information arrive at regular intervals (synchronous) or at random intervals (asynchronous). Between a transmitter (DTE) and a receiver (DCE) wiring is right. RS232 cables can be connected in series.
In configurations where 2 DTE are directly connected, a cable of cross linking or \Null-Modem\ should be used. This cable has female connectors at each end.

mode, six available pins are assigned to the most used RS232

RS232

For a serial line information arrive at regular intervals (synchronous) or at random intervals (asynchronous). Between a transmitter (DTE) and a receiver (DCE) wiring is right. RS232 cables can be connected in series.
In configurations where 2 DTE are directly connected, a cable of cross linking or \Null-Modem\ should be used. This cable has female connectors at each end.

signals. Pins 1 and 6 are however reassigned to lines A and B when the port is used in RS485 mode.
These pins are normally used for the DTR, the terminal ready data and the DSR, willing to establish data signal.

On some models of the PLC, it is possible to mix the RS232

RS232

For a serial line information arrive at regular intervals (synchronous) or at random intervals (asynchronous). Between a transmitter (DTE) and a receiver (DCE) wiring is right. RS232 cables can be connected in series.
In configurations where 2 DTE are directly connected, a cable of cross linking or \Null-Modem\ should be used. This cable has female connectors at each end.

and RS485 communication. When the DSR and DTR signals are not used, the two pins can be used for simultaneous RS485 communication.

RJ11

RJ11

RJ11 – Regitered Jack 11 – is used for the landline. It is an international standard for connecting the fixed telephone to the telecommunications network.
RJ11 uses a 6-slot connector. In this one RJ11 has 6 slots (positions) and two drivers, the standard is written 6P2C. The information transmitted on the line can be digital (DSL) or analog. The telephone cable that arrives at the subscriber has 4 conductors

to RS232

RS232

For a serial line information arrive at regular intervals (synchronous) or at random intervals (asynchronous). Between a transmitter (DTE) and a receiver (DCE) wiring is right. RS232 cables can be connected in series.
In configurations where 2 DTE are directly connected, a cable of cross linking or \Null-Modem\ should be used. This cable has female connectors at each end.

adapters are technically simple.

They are a little expensive, found on the Web or in the specialized shops.