⎯ 7 ⎯
6 F 2 S 0 7 1 5
2.4 Access with a modem via telephone line
Figure 2.4.1 shows the configuration of the RSM system. The PC connects to the front panel of the
relay via two modems and telephone line.
Note that settings of communication speed of both the modem that is closer to the relay and the
relay should be the same speed.
Figure 2.4.1 Access with a modem via telephone line
Figure 2.4.2 shows the configuration of arrangements of the RS232C cables. The left one shows
the straight type and this is used between a PC and a modem, and the right one shows the crossed
type and this is used between a modem and a relay.
The connecting lines represent relationships between the two pins and dotted-lines mean arbitrary
connections.
Figure 2.4.2 Arrangement of RS232C cables
PC
Telephone line
RS232C
D-Sub 25 pins
Modem Modem
D-Sub 9 pins D-Sub 25 pins
D-Sub 9 pins
RS232C
TD 3
RD 2
RTS 7
CTS 8
DSR 6
GND 5
CD 1
DTR 4
RI 9
2 TD
3 RD
4 RTS
5 CTS
6 DSR
7 GND
8 CD
20 DTR
22 RI
DTE D-Sub-9 DCE D-Sub-25
PC
Modem
3 TD
2 RD
7 RTS
8 CTS
6 DSR
5 GND
1 CD
4 DTR
9 RI
TD 2
RD 3
RTS 4
CTS 5
DSR 6
GND 7
CD 8
DTR 20
RI 22
DCE D-Sub-9
DCE D-Sub-25
RelayModem
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