Advantech MOS-1120Y Series, User Manual, Page: 30 / 34

MOS-1120Y/1121Y Series User Manual 22
5.1 RS-232 Signal Wiring
Because the RS-232 interface is not strictly defined, many devices have unique con-
nection methods that may ignore some signal lines or lines reserved for other func-
tions. Therefore, it is best to refer to the installation instructions in the device user
manual.
Generally, data terminal equipment (DTE) refers to a device that communicates with
data circuit-terminating equipment (DCE). DTEs include PCs, terminals, and some
printers, whereas DCEs include modems, digital service units (DSUs), printers, and
laboratory/factory equipment.
In some situations, just three lines may be acceptable: data on TxD, a signal ground,
and a handshaking line. Examples of where this would work are printer or plotter con-
nections, troubleshooting, and situations where only one-wire communication is
required.
For DTE-to-DCE connections, use a straight through cable (i.e., Lines 2 and 3, Lines
4 and 5, and Lines 6 and 20 do not need to be reversed because DCE RS-232 inter-
faces are typically already reversed).
Table 5.1: Terminal or PC (DTE) Connections
DB-25 Male DB-25 Male or Female: Terminal
Pin Signal Pin Signal
2 TxD 3 RxD
3 RxD 2 TxD
4 RTS 5 CTS
5 CTS 4 RTS
6 DSR 20 DTR
7 GND 7 GND
20 DTR 6 DSR
8 DCD 8 DCD
Table 5.2: Modem Connections
DB-25 Male Modem (DCE)
Pin Signal Pin Signal
2 TxD 3 RxD
3 RxD 2 TxD
4 RTS 5 CTS
5 CTS 4 RTS
6 DSR 20 DTR
7 GND 7 GND
20 DTR 6 DSR
8 DCD 8 DCD