Modbus example

Consider a simple example where the PLC sends a part identifier number (P/N) and sets a trigger bit to indicate that it is time to grab the image. In the example, the project returns a PASS bit and a FAIL bit; they will both be cleared to 0 when the trigger bit is detected, and they will have opposite values based on the result of the Status step at the end of processing. The project will also return the X-coordinate, Y-coordinate, and radius values of a detected circle.

Assume the following is the PLC data map. Coils and holding registers are both read from and written to, and have both input and output values. Note that the Matrox Design Assistant offsets are 1-based and inputs and outputs are from the perspective of the PLC.

Coils data table
Field Name	Direction	PLC data map offset	Matrox Design Assistant offset
Trigger	Output	0	1
Reserved	N/A	1...7	N/A
Pass	Input	8	9
Fail	Input	9	10

Holding registers data table
Field Name	Direction	PLC data map offset	Matrox Design Assistant offset
PartID	Output	0	1
Reserved	N/A	1...7	N/A
X	Input	8	9
Y	Input	9	10
Radius	Input	10	11

The values read by the Matrox Design Assistant project are one coil entry and one holding register entry, as defined in the ModbusReader step.

The values written by the Matrox Design Assistant project are 2 coil entries and 3 holding register entries, as defined in the ModbusWriter step. Note that the entry names do not have to be identical, although it is good practice.

Note that Coil number and Register number are set to the Matrox Design Assistant offsets.

The image below displays the Matrox Design Assistant project flowchart.