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Wednesday, May 22, 2019
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SCADA, VB Datafetching from PLC
How to get data from PLC to my VB software through RS 485; have only 1 RS 485 port available.

Deed to get data from PLC (Delta EX2 or Delta SA2) to my VB software (in PC) through RS 485. I have got only 1 RS 485 port available which is connected to SCADA (Advantech). The VB is used only for report generation (SLAVE).


According to the user manual the Delta EX2 supports MODBUS ASCII.

A VB MODBUS ASCII driver/stack to communicate with the device will be needed. Then VB code to read the desired data, format the data, convert the data to a human readable text and output in some form.

Or you could purchase an HMI, like PeakHMI, that only needs configuration and use.


Good luck,

There can only be one master on a RS485 Modbus trunk. Solution is to buy a gateway.

Advantech connects to RS485 port R1
PLC connects to RS485 port R2
PC connects to gateway using ModbusTCP

The gateway will receive requests from the Advantech and from the VB. It will channel these out the port to the PLC and respond to the master. It will merge the requests from both masters so that the PLC thinks there is only one master on the line.

If this interests you, please contact me at

This is very good. I will contact for further explanation