How-To : Set a Word of Bits High

How can i set a whole word of bits high or 1 such as b3:254 in slc and plc 5 systems.

I tried to use a unconditional OTE on a rung with the b3:254 address but it gives me a error and says it must be specified to the bit level?

How else could we accomplish this task?

Provided the individual bits aren't used elsewhere, MOV -1 into B3:254

Thanks

Tim Ganz said:

How can i set a whole word of bits high or 1 such as b3:254 in slc and plc 5 systems.

I tried to use a unconditional OTE on a rung with the b3:254 address but it gives me a error and says it must be specified to the bit level?

How else could we accomplish this task?

Click to expand...

For future reference B3:254 to bit level would be B3:254/1 or /2 or /3 for the relevant bits

Right but i am trying to set every bit in the entire word high.

Why does -1 work i tried 1 but that only turned on the first bit?

Tim Ganz said:

Why does -1 work i tried 1 but that only turned on the first bit?

Click to expand...

To answer your question you need to consider what a word is? For example a 16-bit word is made up of 16 individual bits such as B3:254/00 to B3:254/15. Now if you look at the word in decimal format and you put a "1" in the word, what is the binary equivalent if you look at all the bits in binary format? It is "0000000000000001" because "1" in decimal equals "1" in binary. So now ask yourself what "-1" in decimal is in binary (at least how viewed by an SLC or PLC5)? Hint, the most significant bit (i.e. the 16th bit or B3:254/15) is a sign bit.

It works because 1111111111111111 in twos compliment binary (the kind of numbers computers use) equals -1 in base 10 decimal (the kind of numbers people use).

http://en.wikipedia.org/wiki/2s_compliment