plc ladder logic help

[racinilodge]

hello, i'am trying to write logic where by 2 dock doors are used, if a first dock door is open, the second cant open, till the first is closed, so that both cant be open together, but can be closed together. i was wondering how i go about writing the ladder logic for this situation, and what i need to do to make this occur? your help is grealty appreciated,
thank you, mike.

 

[Macbeth]

What I/O point do you have avalible to you? do you have door open/close limit switches of any kind? Or just the buttons.
If you have just the buttons then your get'n in trouble. What I mean is you will be realing on the last action that ocured. When the PLC powerd up it would have to assume bolth doors are aready closed and that may not be so.

When you say they can not open togeter do you mean they can not be open at the same time (like an air lock) or that they can not open at the same time (the dam breaker trips)?

 

[Macbeth]

Opps, I see like an air lock.