Advantech PCI-1625U user manual Modem Connections

Table 5.6: Modem Connections

DB25 Male		Modem (DCE)
Pin	Signal	Pin	Signal
2	TxD	2	RxD
3	RxD	3	TxD
4	RTS	4	CTS
5	CTS	5	RTS
6	DSR	6	DTR
7	GND	7	GND
20	DTR	20	DSR
8	DCD	8	DCD

For DTE to DCE connections, use straight-through cable (i.e., you don't have to reverse lines 2 and 3, lines 4 and 5, and lines 6 and 20 since, in general, the DCE RS-232 interfaces are reversed themselves).

Table 5.7: Terminal without Handshake

DB-25 Male		Terminal, PC (DTE)
Pin	Signal	Pin	Signal
2	TxD	3	RxD
3	RxD	2	TxD

4RTS —

5CTS —

7	GND	7	GND
6	DSR —
20	DTR —

8DCD —

Therefore, if you are not using CTS, RTS, DSR, DTR and DCD signals, please short pins 4 and 5 together, and please short pins 6, 8, and 20 together.

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