G.18
SEL-387-0, -5, -6 Relay Instruction Manual Date Code 20170601
Distributed Network Protocol
Point Remapping
The DNP command will report an error if an index is used twice, an invalid
index is used, or nonnumeric data are entered:
xx is referenced more than once, changes not saved
xx is not a valid index, changes not saved
Invalid format, changes not saved
Custom Scaling
In addition to remapping, these commands can be used on analog inputs to
create custom scaling and dead-bands per point. Scaling is done by adding a
semicolon and scaling factor to a point reference. The base value will be
multiplied by the scaling factor before reporting it. This is done instead of the
DECPLA setting that would normally apply. Dead-bands are added using a
colon and dead-band count. This dead-band will override the ANADBA
setting. For example:
==>DNP AI <Enter>
Enter the new DNP Analog Input map
112;5 28;0.2 17:10 1;1:15 <Enter>
==>
These settings will cause the value at index 112 (now at index 0) to be
multiplied by five before it is reported. Similarly, the value at index 28 (now at
index 1) will be multiplied by 0.2 before it is reported. Both of these values
will use the default dead-band. The value at index 17 (now at index 2) is left
for default scaling, but uses a dead-band of +/– 10 counts. Similarly, the value
that was at index 1 (now at index 3) is now scaled by 1 and uses a dead-band
of +/– 15 counts.
Modem Support
The modem handling will only be applied when the port settings include the
following:
PROTOCOL = DNP
MODEM = Y
On power-up and settings change, the relay shall initialize the modem by
issuing the string “+++AT” followed by the MSTR string and <CR>. This will
initialize the modem. The MSTR (modem string) is a port setting visible only
when the protocol setting is DNP. The MSTR setting is a series of ASCII
characters that initialize the modem by sending the modem a series of
commands.
If someone calls in, the modem will send “RING” and “CONNECT”
messages to the relay. These messages, as well as all messages received while
DCD is low, shall be ignored. All DNP messages received while connected
shall be treated normally.
If the relay needs to send an unsolicited message and it is not currently
connected, it must attempt to make a connection by sending the string
“+++ATDT” followed by the phone number and <CR>. It shall then wait for a
“CONNECT” message. Once “CONNECT” is received and CTS is asserted,
the relay can consider itself connected and continue its transaction. If
connection is not achieved within MDTIME seconds of initiating the phone
call, the relay shall issue the command “+++ATH<CR>” and wait at least
NOTE 1: Because of the connection
requirements described here, it will
not be possible to use hardware flow
control (RTSCTS) with the modem.
This means that it is important to
select a port baud rate low enough
that the modem connection will not
end up slower, or there will be a high
likelihood of losing characters.
NOTE 2: The CTS signal shall be
treated as a data carrier detect (DCD).
This means that the message can only
be transmitted while DCD is asserted.
(Normally, a modem will be connected
with a C220 or C222 cable that ties
the DCD of the modem to the CTS.)
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