An RS232 connection occurs between two devices, a “Data Terminal Equipment” (DTE), among which, for example, computers and terminals can be mentioned; and another, typically a “Data Communications Equipment” (DCE), including modems or printers. It is important to always know whether the device being connected is a DTE or a DCE, to determine the signals and their direction on the interface connector. In our production you can find a wide range of interconnection cables between the different devices.
Serial line signals
Initially, the serial line signals were assigned for the 25-pin connector, and the ability to assign a second channel was also provided. However, only one channel has always been used and, for this reason, over time, there has been an orientation towards the use of smaller connectors with a lower number of pins. The signals of the standard RS232 connection are shown in the following table:
Name | Description | DTE | DCE | DB25 | DB9 | DIN 8 | RJ45 |
All connectors are seen from the front | |||||||
FG | Frame ground | 1 | |||||
TD | Transmitted data | Oct | In | 2 | 3 | 3 | 6 |
RD | Received data | In | Oct | 3 | 2 | 5 | 5 |
RTS | Request to send | Oct | In | 4 | 7 | 6 | 8 |
CTS | Clear to send | In | Oct | 5 | 8 | 2 | 7 |
DSR | Data set ready | In | Oct | 6 | 6 | ||
SG | Signal ground | 7 | 5 | 4,8 | 4 | ||
DCD | Data carrier detected | In | Oct | 8 | 1 | 7 | 2 |
Positive voltage | 9 | ||||||
Negative voltage | 10 | ||||||
Unassigned | 11 | ||||||
SDCD | Secondary DCD | In | Oct | 12 | |||
SCTS | Secondary CTS | In | Oct | 13 | |||
STD | Secondary TD | Oct | In | 14 | |||
TC | Transmit clock | In | Oct |
15 |
|||
SRD | Secondary RD | In | Oct | 16 | |||
RC | Receive clock | In | Oct | 17 | |||
Unassigned | 18 | ||||||
SRTS | Secondary RTS | Oct | In | 19 | |||
DTR | Data terminal ready | Oct | In | 20 | 4 | 1 | 3 |
SQ | Signal quality detector | 21 | |||||
RI | Ring indicator | In | Oct | 22 | 9 | ||
DRS | Data rate selector | 23 | |||||
SCTE | Serial clock transmit external | Oct | In | 24 | |||
BUSY | Busy | 25 |
RS232 connectors
For convenience, we show a view of the connectors for the RS232 connection which the commonly used devices are equipped with.
DTE Equipment) Personal computer DB 9 male connector | Pin | Direction | Signal | Description |
1 | In | DCD | Data carrier detect | |
2 | In | RD | Receive data | |
3 | Oct | TD | Transmit data | |
4 | Oct | DTR | Data terminal ready | |
5 | GND | Signal ground | ||
6 | In | DSR | Data set ready | |
7 | Oct | RTS | Request to send | |
8 | In | CTS | Clear to send | |
9 | In | RI | Ring indicator | |
(DCE Equipment) DB Modem 9 female connector | Pin | Direction | Signal | Description |
1 | Oct | DCD | Data carrier detect | |
2 | Oct | TD | Transmit data | |
3 | In | RD | Receive data | |
4 | In | DTR | Data terminal ready | |
5 | GND | Signal ground | ||
6 | Oct | DSR | Data set ready | |
7 | In | CTS | Clear to send | |
8 | Oct | RTS | Request to send | |
9 | Oct | RI | Ring indicator | |
(DTE Equipment) ELSIST products RJ45 8pin female connector | Pin | Direction | Signal | Description |
1 | ||||
2 | In | DCD | Data carrier detect | |
3 | Oct | DTR | Data terminal ready | |
4 | GND | Signal ground | ||
5 | In | RD | Receive data | |
6 | Oct | TD | Transmit data | |
7 | In | CTS | Clear to send | |
8 | Oct | RTS | Request to send |