SIEMENS CPU2xx

I am wondering why Siemens CPU2xx do not have normal timers for use and they only have Delay ON or OFF timers.

Ok, I'll bite.

What do you consider to be a "normal" timer? I always thought of Delay On and Delay Off as pretty normal.

Steve

Siemens Cpu2xx timers

When I say a normal timer I mean a timer that will turn on immediately when its input is high,for a preset period without the need to make its input low.

Try this code:

I use an off delay time which is controled by an edge triggerd input
Every time I0.0 turns from 0-->1, the timer starts!

Network 1

LD I0.0
EU
TOF T37, +30

Network 2

LD T37
= Q0.0

Leonardo!

I may be wrong here but it could be that you misunderstand what is meant by On Delay and Off Delay.

Both timers do exactly what you describe when you say "turn on immediately when its input is high,for a preset period without the need to make its input low". The terms "On-Delay" and "Off-Delay" refer to the timers' output. This maybe where your confusion is.

The TON element in the S7-216, for instance, has two variable elements; IN and PT. These refer to enable INput and the Preset Time. The following is the description of its operation taken directly from the Micro/Win 32 help file:

"The On-Delay Timer (TON) instruction counts time when the enabling input is ON. When the current value (Txxx) is greater than or equal to the preset time (PT), the timer bit is ON"

So, if you have an on timer (T37), once the IN is satisfied, the timer starts timing for the preset period, PT. Once the timed value is greater that the preset, the timer bit, T37, is on. You can then use XIO and XIC elements for this element throughout your program.

            ____T37____

   I1.1    |           |

---| |-----|IN      TON|

           |           |         

       30  |PT         |

           |___________|



   T37      M0.1

---| |------( )-





   T37      M0.2

---|/|------( )-

Now, In this little program, input I1.1 is either off or on.

When I1.1 is low, bit T37 is low, M0.1 is low, and M0.2 is high .

When I1.1 initially goes high, the timer starts timing but bit T37 is still low, M0.1 is still low, and M0.2 is still high.

After 3 seconds (T37 is a 100ms time-based timer) of I1.1 being high, bit T37 goes high, M0.1 goes high, and M0.2 goes low.

As soon as I1.1 goes low again, bit T37 goes low, M0.1 goes low and M0.2 goes high.

Does that help?
Steve