D.10
SEL-751 Relay Instruction Manual Date Code 20170927
DNP3 Communications
DNP3 in the SEL-751
synchronization periodically by setting the TIMERQn setting to the desired
period. You can also set it to not request, but accept, time synchronization
(TIMERQn = M for “master”).
Modem Support
The SEL-751 DNP implementation includes modem support for serial ports.
Your DNP3 master can dial-in to the SEL-751 and establish a DNP3
connection. The SEL-751 can automatically dial out and deliver unsolicited
DNP3 event data.
When the device dials out, it waits for the “CONNECT” message from the
local modem and for assertion of the device CTS line before continuing the
DNP transaction. This requires a connection from the modem DCD to the
device CTS line.
NOTE: Contact SEL for information
on serial cable configurations and
requirements for connecting your
SEL-751 to other devices.
You can either connect the modem to a computer and configure it before
connecting it to the SEL-751, or program the appropriate modem setup string
in the modem startup string setting MSTR. You should use the PH_NUM1
and (optional) PH_NUM2 settings to set the phone numbers that you want the
SEL-751 to call. The SEL-751 automatically sends the ATDT modem dial
command and then the contents of the PH_NUM1 setting when dialing the
modem. If PH_NUM2 is set, use the RETRY1 setting to configure the number
of times the SEL-751 tries to dial PH_NUM1 before dialing PH_NUM2.
Similarly, the RETRY2 setting is the number of attempts the SEL-751 tries to
dial PH_NUM2 before trying PH_NUM1. MDTIME sets the length of time
from initiating the call to declaring it failed because of no connection, and
MDRET sets the time between dial-out attempts.
NOTE: RTS/CTS hardware flow
control is not available for a DNP3
modem connection. You must use
either X-ON/X-OFF software flow
control or set the port data speed
slower than the effective data rate of
the modem.
The settings PH_NUM1 and PH_NUM2 must conform to the AT modem
command set dialing string standard, including:
➤ A comma (,) inserts a four second pause
➤ If necessary, use a 9 to reach an outside line
➤ Include a 1 and the area code if the number requires long
distance access
➤ Add any special codes your telephone service provider
designates to block call waiting and other telephone line
features.
DNP3 Settings
The DNP3 port configuration settings available on the SEL-751 are shown in
Table D.7. You can enable DNP3 on Ethernet Port 1 or on any of the serial
ports 2 through 4, for a maximum of five concurrent DNP3 sessions. Each
session defines the characteristics of the connected DNP3 Master, to which
you assign one of the three available custom maps. Some settings only apply
to DNP3 LAN/WAN, and are visible only when configuring the Ethernet Port.
For example, you only have the ability to define multiple sessions on port 1,
the Ethernet port. Likewise, settings applicable to serial DNP3 are visible only
when configuring a serial port.
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