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Reading and Writing in the ACE PLC with Modbus


We will see how to read in ACE PLC a Bit and Word in Modbus via the ACE USB port with a Windows Modbus software

Creating a small test program to automatically change the bit and word

Add these MyBit and MyWord tags in ACE Modbus register, then, upload and run the ACE program

Close the vBuilder software, otherwise the COM port will be busy.


Read with Modbus Doctor software (Master Modbus)

Download Modbus Doctor and run it In Windows Device Manager, search the COM port number of your ACE PLC

Select the right COM port and RTU protocol in Modbus Doctor

Select Slave 1, Register 0, Lenght 1 and Type 3 Holding registers for read the Word

Select Slave 1, Register 0, Lenght 1 and Type 1 Coil status for read the Bit


Write in ACE PLC

to do this, you must allow writing in vBuilder by checking the “Remote Writable” function

Then, you can write inside the ACE PLC in Modbus

Note: We have 256 byte transmit and receive buffers. A message longer than 256 byte could be received and clobber some variable that is critical


Modbus-TCP via the ACE-GTW Modbus Gateway

The operation is the same, just select Modbus-TCP instead of Modbus RTU in Modbus-Doctor.