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8 LOCAL USER INTERFACE
•
S0=1: the relay modem answers incoming calls after one ring. S0 can be set for any value between 1 and
255, if it is desirable to delay modem answering. Note that ALPS-LINK (version 1.05 or higher) configures
the PC modem to wait 60 seconds for the relay modem to answer. If the relay modem register S0 is set
higher than 12 (answer after 12 rings), the PC modem may time out and hang up before the relay modem
can answer. S0=12 corresponds approximately to the 60 second delay (S7=60) at the PC modem; how-
ever, you should verify the number of rings that correspond to 60 seconds for a particular application.
Table 8–7 lists the modem command set required to communicate to the relay from a remote PC.
A PC can be connected directly to the relay without a modem through a null-modem cable. The required pin-to-
pin connections for the PC null-modem cable are shown below in Figure 8–4: 25-PIN NULL MODEM CABLE.
The pin-to-pin connections for a null-modem cable to the 9-pin connector on the KEYPAD/DISPLAY INTER-
FACE are shown below in Figure 8–5: NULL MODEM CABLE FOR PORT PL1. The null modem cable should
be no more than 50 feet long.
TD
2
RD
3
RTS
4
CTS
5
DCD
8
DSR
6
RI
22
DTR
20
G N D
7
TO RELAY
PL-2 & 3
TD
2
RD
3
DSR
6
RI
9
DTR
4
RTS
7
CTS
8
DCD
1
G N D
5
TO RELAY
PL-1
GE Power Management
REMOTE COMMUNICATIONS PC DIRECTLY
NULL MODEM CABLE
Figure 8–4: 25-PIN NULL MODEM CABLE
REMOTE COMMUNICATIONS FROM PL-1 MODULE
NULL MODEM CABLE
Figure 8–5: NULL MODEM CABLE FOR PORT PL1
LPS-D Line Protection System
8.4 REMOTE COMMUNICATION INTERFACE
8.4.5 NULL-MODEM CONNECTIONS
2
TD
3
RD
4
RTS
5
CTS
8
DCD
6
DSR
22
RI
20
DTR
7
G N D
TO PC
2
TD
3
RD
6
DSR
9
RI
4
DTR
7
RTS
8
8
CTS
1
DCD
5
G N D
TO PC
8-
31
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