Step7 Step Sequencer Questions

Hi All,

I've been doing a little reading here on Step Sequencers-State Machines before I begin to implement a rather lenghtly one for a project before me.

The sequences are not complex only requiring a number of activations of valves, pumps etc when certain conditions are met. They could be however 50 steps in sequence.

http://www.plctalk.net/qanda/showthread.php?t=45009&highlight=step+sequencer+S7&page=2

I've been reading this thread with interest and decided to run with Manglemenders example of using an input Word and an output word to ensure each step remains active for at least one scan. This makes sense and I have to admit in some smaller projects throughout the years I may have not considered this. I've always opted to use a single Word for step status and evalulated this on each rung as a permissive for activations.

Now on to my questions...

1. I need to have a timer (watch dog of some sort) running during each step. If possible I would like to use a single timer and change its preset after each transition. This will be used to either step on or fault the sequence.
How can I detect that the sequence has stepped on using the logic (FC21) posted in above link.

2. The client has requested the ability to Hold/StepOn/StepBack the sequence. Is this possible to implement this using this logic?

Please ignore my first question...

To detect a change of state I was comparing the Input Word to Output Word and if they were not equal then the timer would reset. It wouldnt work but the rung should have been before the last rung were I copy the Outputword into the input word!