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8.8
EXAMPLE 7 demonstrates the DATAFLOW RTU as a MODBUS device using stored
data access. The configuration consists of a remote RTU with another RTU connected to a
MODBUS controller. Example 7 uses RTU Programming Software as the MODBUS
controller. The remote RTU and the RTU connected to the MODBUS controller each have
five digital inputs and one analog input.
NOTE:
In real applications the MODBUS controller is a PLC or a SCADA program
operating with a MODBUS driver.
8.8.1 RTU ID 1 SETUP: Example 7 requires oneDATAFLOW RTUto be wired and its hard
ware configured according to Figure B 12 - EXAMPLE 6 ID 1 Wiring Diagram on page
B-36. Load Software Programming configuration file EXP71D1.USR into RTU ID 1.
8.8.2 RTU ID 2 SETUP: Example 7 requires the other DATAFLOW RTU to be wired and its
hardware configured according to Figure B 13 - EXAMPLE 6 ID 2 Wiring Diagram on
page B-37. Load Software Programming configuration file EXP71D2.USR into RTU ID 2.
NOTE:
Except the configuration files, these two setups are identical to Example 6.
8.8.3 EXPLANATION: Although the RTU can operate in two different MODBUS modes,
Example 7 deals with stored access only. In this mode, only the RTU connected to the
MODBUS controller is polled, eliminating the need for RF polling.
8.8.4 Examine the configuration of RTU ID I. It is no longer in control of the process and is
simply a MODBUS device controlled by the MODBUS controller:
•
XMIT CHECK IN is set to 0.
•
SEND LIST is all O's.
•
REPEAT LIST is all O's.
•
All inputs have INITIATE XMIT set to NO.
•
All outputs have USED set to NO.
Examine the configuration of RTU ID 2. It controls activation of RTU ID l.
•
XMIT CHECK IN is set to 30 seconds.
•
SEND LIST is set to 1.
•
REPEAT LIST is all O's.
•
All inputs have INITIATE XMIT set to YES.
•
All outputs have USED set to NO.
Examine the SCADA CONFIG screen display for RTU ID l. All entries in the
NOTE:
list are 0 because no RF p olling is talcing place.
8.8.5 Example 7 demonstrates polling by stored access, using the RTU Programming Software
as the MODBUS controller. To examine the polling method, execute the EXTERNAL
BLOCK EDIT option from the UTILITIES screen.
•
Set the ID to 01 and the PAGE ADDRESS to 10. Execute the UPLOAD command.
Examine memory locations 1089 to 108E. These values are the current state of RTU
ID 2 inputs 6 to 1.
•
Memory location 108F is a message counter. This value is incremented every time
RTU ID 1 receives a valid message from RTU ID 2.
Change the inputs on RTU ID 2 while continuously executing the UPLOAD command.
Watch the 1089 to 108F memory locations update each time.
Software/ Programm
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EXAMPLE?
( B-24)
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