RS232 - All about

rs232 cable
rs232 cable

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.

25-pin Null-Modem RS232 connection diagram :

1 MASS 1
2 ISSUE DATA 3 CROSSING
3 RECEPTION DATA 2 CROSSING
4 REQUEST TRANSMISSION 5 CROSSING
5 READY FOR TRANSMISSION 4 CROSSING
6 READY DATA 20 CROSSING
7 0 VOLT ELECTRIC 7
8 ONLINE SIGNAL DETECTION 8 CROSSING
9 (+) TENSION 9
10 (-) TENSION 10
11
12 2° - SIGNAL DETECTION 12
13 2° - READY FOR TRANSMISSION 13 CROSSING
14 2° - TRANSMISSION OF DATA 14 CROSSING
15 DCE - CLOCK SIGNAL FOR TRANSMISSION 17 CROSSING
16 2° - RECEIPT OF DATA 16 CROSSING
17 CLOCK SIGNAL FOR RECEPTION 24 CROSSING
18 DTE - REQUEST FOR THE LOCAL DCE TO BE RECEDED
19 2° - TRANSMISSION 19 CROSSING
20 DATA SENT 6 CROSSING
21 TRANSMISSION QUALITY SIGNAL 21
22 RINGTONE INDICATOR 22
23 SPEED SELECTION SIGNAL 23
24 DCE - CLOCK SIGNAL FOR TRANSMISSION 24 CROSSING

Connector rs232 25 pins
Connector rs232 25 pins

RS232 UART

To establish communication by an RS232 cable, it is necessary to define the protocol used, in particular the tau of transmission and coding.
In practice UART is the most used.
UART RS232 includes 9 records of 8-bit sorted into three categories :

- Control records : IER, LCR, MCR, DL (16-bit : + DLL DLM).
- Records of States : LSR, MSR and IIR.
- Data : RBR and THR.
rs232 9 pins connector
rs232 9 pins connector

Conversion : DB25 - DB9

The original pinout RS232 was developed for 25-pin (sub-d). Today 9 pins RS232 connectors are commonly used.
In mixed applications, a 9-to-25 converter can be used.
DB9 DB25 FUNCTION
1 8 DETECTED DATA CARRIER
2 3 RECEIVE DATA
3 2 DATA TRANSMISSION
4 20 READY DATA TERMINAL
5 7 SIGNAL MASS
6 6 READY DATA
7 4 REQUEST TO SEND
8 5 CLEAR TO SEND


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