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8.4 REMOTE COMMUNICATION INTERFACE
The S7=60 command is present starting with version 1.05 of ALPS-Link. Earlier versions of ALPS-Link do not
send this command, leaving the time out at the default value, which is typically 30 seconds.
If any of the above commands are not recognized by the modem, then the modem will not operate properly. In
addition to the required configuration settings listed in Table 8–4, it is suggested that the following two settings
also be made:
&D3: the modem resets on the ON-to-OFF transition of DTR (Data Terminal Ready).
&C1: DCD (Data Carrier Detect) tracks the received carrier signal.
The modem will operate properly without these two settings, but it will not hang up if the appropriate handshak-
ing signal is lost.
An ALPS-Link setting establishes the baud rate, which must match the baud rate setting of the LPS-D. ALPS-
Link will then set the specified PC serial port (COM1, COM2) to the proper baud rate, parity, data bits, and stop
bits. If the PC modem is capable of operating at more than one baud rate, then it must be able to automatically
configure its baud rate, character length, and parity setting by examining the "AT" command prefix.
The LPS-D modem must be configured for "dumb" (command recognition disabled) operation. On the Hayes
V-Series 2400 SmartModem, this setting is made with an internal jumper. Since the relay sends no configura-
tion commands to its modem, the required configuration settings must be made before connecting the modem
to the relay. Additionally, the modem must be initialized to the required configuration settings each time modem
power is turned OFF and then ON. Depending on the design of the modem this is accomplished with switch
settings via switches or by saving the settings in nonvolatile memory.
The required configuration settings are listed in Table 8–5: CONFIGURATION SETTINGS FOR THE MODEM
CONNECTED TO THE RELAY.
Table 8–5: CONFIGURATION SETTINGS FOR THE MODEM CONNECTED TO THE RELAY
Command
Description
E0
Disable command state echo
L0
Low speaker volume (desirable, not required)
Q1
Disable result code display
&C1
DCD (Data Carrier Detect) tracks the received signal
&D0
Modem resets on the ON-OFF transition of DTR (Data Terminal Ready)
&Q0
Asynchronous mode
8
S0=1
Enable auto-answer
If any of the settings in Table 8–5 cannot be implemented the modem may not answer, the relay may not con-
nect properly, or you may not be able to log into the relay. With a Hayes V-Series 2400 SmartModem or equiv-
alent, the relay modem performs a modulation handshake with the PC modem to set the baud rate of the relay
modem. The default setting of N1 permits handshaking to occur at any baud rate supported by both modems.
This is one reason why it is better to use identical modems at each end.
Note that auto-answering is controlled by register S0:
•
S0=0: disables auto-answer.
8-
30
LPS-D Line Protection System
8 LOCAL USER INTERFACE
8.4.4 LPS-D MODEM
GE Power Management
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