Please suggest how I can read a 16 bit value from a Modbus holding register, using a Network Analog input, modify bit 2 without altering the other bits, and write back to the holding register with Network Analog output.

My first thoughts are to use a Shift Register to move Bit 2 to the output, then modify the output. How do I then write the bit back to the shift register?

Any suggestions or examples would be appreciated.

Stephen

I need to read the data word from Modbus, if bit 2 is not set then set it, if it is set then clear it, then write back to Modbus. The Modbus device needs to see a rising edge on bit 2 when I activate an input on the Logo. Other bits of the data word need to be unchanged.

Stephen

This is my attempt, but needs lots of blocks to get down to bit 2. Zip of complete code attached, this shows the top two bits. There has to be a simpler way of doing it, but I cannot think of it at the moment.

For if/then I am using an comparator, and selecting the required value using a multiplexer. If the value is zero, then it will only set the bit if a button is pressed at that time.

Like this, picture here, code at the bottom of the page in the zip file

If you know a simpler way of splitting an analogue value into binary as in the rest of the code, I would really appreciate knowing how it works.

Stephen

I am sorry, I meant to address the points in your post. You said "Logo does not offer the option of "If..then", so I said:

"For if/then I am using an comparator, and selecting the required value using a multiplexer. If the value is zero, then it will only set the bit if a button is pressed at that time.

Like this, picture here, code at the bottom of the page in the zip file"

and I explained that it would not be constantly set and reset as it needs the button to be pressed.

This was not the problem I had, it was just context. The problem I had was trying to split an integer analog value into bits, without taking up a lot of code space. The code example I attached achieves what I need, but I am sure there must be an efficient way to achieve it.

Apologies if I seemed to ignore what you said.

Stephen