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Modbus Serial Gateway

This tutorial is intended as a supplement to the original manuals for the products. Therefore, use it as a means to familiarise yourself with the product, and not as a guide for a complete installation.
Product Information
The following is an example of how to change the rate on a frequency converter connected to a PLC's SCU card via 2-wire Modbus.
First, we switch off the termination resistance in accordance with the instructions below.
selecting termination resistance
Then we connect the cable between the PLC and converter (s).
PLC Inverter
PLC  Inverter

Pair the 2-wire  R + S + and R-S-. These are associated with the RDB and the RDA for the PLC. Remember to put the switch on the 2-wire.
The 4-wire is connected to RDB S +, S-RDA, SDB to the R + and R-SDA to. Remember to put the switch on the 4-wire.

This function block transfers speed and direction to the frequency converter's node 4. The rate is show in Hz as a floating-point in the D1040. D1042 defines the area where the FWD and REV = 0 = 1. Bit 404.00 must be enabled to transfer the data. The function block does not work alone. It is necessary to have a Refresh to keep up the communication. A common Refresh is enoug for a network with multiple converters. Refresh is described on the next page.

In the example we have set UnitNo on SCU module to 2. We use the top port on the module (ie 1 I scan list) we have set bit 4 (# 00000010hex) to activate the node 4 on the Modbus. Model Type I has option 0 for node 4, in other words MV/V7. The recommended interval count is between 20 and 100, depending on the space on the Bus. CIO 500-563 and E0-44 is reserved for communication and status for all nodes. 
These 2 commands are all we need to program to manage the speed for an inverter.
The next step is to activate serial port 1 on the Serial Gateway so that it opens for Modbus communication. This is done by going into the IO Table. Press Create, then double-click on the module. The following screen is filled in and transferred to the PLC.

Setting the frequency converter

In the adapter must set the following parameters:

3G3MV/V7 3G3JV/J7 3G3PV/RV/E7/F7  
n001 4 n001 1 A1-01 2 To access the parameters below
n003 2 n002 2 b1-02 2 Modbus, RUN-command
n004 6 n003 6 b1-01 2 Modbus F.ref selection
n151 3 n68 3     Serial Fault Action (3=Alarm is displayed)
        H5-04 3 Serial Fault Action (3=Continue operation)
n152 1 n69 1 o1-03 0 Frequency unit (MV/JV=0.01Hz, PV/RV=0.01Hz)
n153 x n70 x H5-01 x Replace x with your own Slave number (1-31) for each converter
n154 2 n71 2     Baudrate (19200) (0=2400, 1=4800, 2=9600, 3=19200)
        H5-02 3 Baudrate (19200) (1=2400, 2=4800, 3=9600, 4=19200)
n155 2 n72 2     Parity (No parity) (0=E, 1=O, 2=N)
        H5-03 0 Parity (No parity) (0=N, 1=E, 2=O)
        H5-05 1 Serial Fault Detect (0=No, 1=Yes)
n156 10 n73 10 H5-06 10 Send wait (ms)
n157 0 n74 0     RTS Control (0=ON when sending, 1=Disabled)
        H5-07 1 RTS Control (0=Disabled, 1=ON when sending)

RTS Control is used in 2-wire RS485 or when there is more than 1 slave.
Set n001 or A1-01 back to 1 after the configuration is done. Turn the power on the power adapter for it to be updated with the new settings.

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Created 2008-11-19
Modified 2008-11-26
Views 9504


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