Add Instruction in Ladder Logic

ADD - Adding

When rung conditions are true, this output instruction adds Source A to Source B and stores the result at the destination address. Source A and Source B can either be values or addresses that contain values, however Source A and Source B cannot both be constants.

Example 1

N7:0 = N7:0 + 5

Ladder Logic Solution

Source A = N7:0 = 830 , Source B = 5 , Destination = N7:0 = 835

Example 2

N7:3 = N7:1 + N7:2

Ladder Logic Solution

Source A = N7:1 = 32000 , Source B = N7:2 = 32000, Destination = -1536 (why).

This is because the result of the addition could not fit in 16 bit register, and therefore we have the overflow bit on.

Clearing minor error that might be generated if we have an overflow.

Note:

• If the destination value is > 32767 then the overflow bit S:0/1 bit will be set hence setting the minor bit error S:5/0. If this bit is not cleared then it will case major error.
• Cant program Source A and Source B as constant, at least one of them should be a variable.