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CHAPTER 5: COMMUNICATIONS
EPM 6000 MULTI-FUNCTION POWER METERING SYSTEM – USER GUIDE 5–13
5.3 DNP Implementation
5.3.1 Overview
The EPM 6000 meter is capable of using RS485 as the physical layer. This is accomplished
by connecting a PC to the meter with the RS485 connection on the back face.
RS485 provides multi-drop network communication capabilities. Multiple meters may be
placed on the same bus, allowing for a master device to communicate with any of the
other devices. Appropriate network configuration and termination should be evaluated for
each installation to insure optimal performance.
The EPM 6000 communicates in DNP 3.0 using the following communications settings: 8
data bits, no parity, and 1 stop bit. The EPM 6000 can be programmed to use several
standard baud rates, including: 9600, 19200, 38400, and 57600 bps.
5.3.2 Data Link Layer
The Data Link Layer as implemented on the EPM 6000 is subject to the following
considerations.
The control byte contains several bits and a function code. Communications directed to
the meter should be primary master messages (DIR = 1, PRM = 1). Responses will be
primary non-master messages (DIR = 0, PRM = 1). Acknowledgment will be secondary non-
master messages (DIR = 0, PRM = 0).
The EPM 6000 supports all of function codes for DNP 3.0:
• Reset of Data Link (function 0): Before confirmed communication with a master
device, the data link layer must be reset. This is necessary after a meter has been
restarted, either by applying power or reprogramming the meter. The meter must
receive a RESET command before confirmed communication may take place.
Unconfirmed communication is always possible and does not require a RESET
command.
• User Data (function 3): After receiving a request for USER DATA, the meter will
generate a data link CONFIRMATION, signaling the reception of that request, before
the actual request is processed. If a response is required, it will also be sent as
UNCONFIRMED USER DATA.
• Unconfirmed User Data (function 4): After receiving a request for UNCONFIRMED
USER DATA, a response will be sent as UNCONFIRMED USER DATA if required.
DNP 3.0 allows for addresses from 0 to 65534 (0000h to FFFEh) for individual device
identification, with the address 65535 (FFFFh) defined as an all stations address. Addresses
are programmable from 0 to 247 (0000h to 00F7h), and recognize address 65535 (FFFFh)
as the all stations address.
5.3.3 Transport Layer
Multiple-frame messages are not allowed for the EPM 6000. Each transport header should
indicate it is both the first frame (FIR = 1) and the final frame (FIN = 1)