GE EPM 6000 Multi-function Power Metering System DNP Implementation, Data Link Layer

CHAPTER 5: COMMUNICATIONS

5.3DNP 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.

5.3.2Data 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.

5.3.3Transport 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)

EPM 6000 MULTI-FUNCTION POWER METERING SYSTEM – USER GUIDE 5–13