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18
SCADA (MODBUS) DATA LINK (EMCP 3.2 & 3.3)
The SCADA DATA LINK or MODBUS is supported by the EMCP 3.2 and EMCP 3.3. The EMCP 3.2 and EMCP 3.3 have a SUPERVISORY CONTROL AND DATA ACQUISITION (SCADA) communications link between the controller and a host device using the MODBUS protocol. The host device is able to remotely monitor or control the genset package equipped with the EMCP 3 GSC in much the same way an operator does from the panel. •
The host device connects to the EMCP GSC through a half-duplex RS-485 serial link.
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The data is transmitted in a binary format over the serial connection.
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The host device acts as Modbus Master, and the EMCP 3 GSC acts as the Modbus Slave, also called a REMOTE TRANSMITTER UNIT (RTU).
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The host device initiates all communication, sending commands or requests for information to the EMCP 3.2
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The EMCP 3 GSC then takes action based on the query and/or sends a response to the query over Modbus.
Baud rates can be configured on the EMCP 3 GSC. Various data rates between 2400 bits/second (baud) and 57,600 bits/second are available. See the SOFTWARE CONFIGURATION Chapter 0 below for instructions. WIRING SCADA COMMUNICATION wires are brought out of the EMCP 3 GSC as part of the 70-pin AMP connector. Table 12 shows the pins on the AMP connector. TABLE 12 SCADA PINS ON 70-PIN CONNECTOR SCADA COMMUNICATION WIRES Pin # Name
Description
3
MODBUS –
Optically isolated half-duplex differential (-) for Modbus
4
MODBUS Reference
Half-duplex RS-485 Reference for Modbus
5
MODBUS +
Optically isolated half-duplex differential (+) for Modbus
MODBUS DATA TRANSMISSION over RS-485 is accomplished over a single shielded twisted pair for differential signaling with transmit and receive alternating over the same wire pair (MODBUS+ and MODBUS-). The Reference (MODBUS REF) should be connected to the shield, to prevent ground loop currents. •
FIGURE 71 shows a possible wiring configuration to a RS-485 device.
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FIGURE 72 shows a possible wiring configuration to a RS-485 to RS-232 converter.
NOTE: See documentation of connected device to verify wiring configuration.
18 SCADA (Modbus) Data Link (EMCP 3.2 & 3.3)
