counting bits

[godfrey]

I have 4 bits B3:0/0 thru B3:0/3 that each represent a unit being on. I want to count the number of bits set to one and return an integer between 0 and 4 representing the number of units on. Without doing it the long way (16 separate rungs with IF and MOV statements) is there something simpler? I'm using a SLC 5/05.

 

[bernie_carlton]

5 lines, 1 rung:

1 - Clear a register (let's say N7:0)
2. - If bit 1 then add 1 to N7:0
3. - If bit 2 then add 1 to N7:0
4. - If bit 3 then add 1 to N7:0
5. - If bit 4 then add 1 to N7:0

 

[Terry Woods]

Maintain a "Unit-ON" count.

Each time you turn one of the units ON, ADD 1 to Vxxx.
Each time you turn one of the units OFF, SUB 1 from Vxxx.

To see current ON-Status, read Vxxx.