You can probaly program you scanner to send a tab after a scan
If the scanner is used for somethign else where this would be undesirable
The easiest way is proably working with messages.
- A scripts in the onChange of the inputfield, that sends its step number/id in a message to the page
- In the page a message handler that sends a message to the next step
- a message handler on the inputfield that does a focus if its id matches the one send by the message of step 2
it can also be done with a step less if you use indexs instead of your prefex
example: