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.
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.
Then we connect the cable between the PLC and converter (s).
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.
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.
Setting the frequency converter
RTS Control is used in 2-wire RS485 or when there is more than 1 slave.