Shift Registers- How do you "Wrap Around"when you use all your bits ?

Good Morning ,


I need to use a shift register to keep track of good and bad parts . As a rough draft I'm using 300 bits. When the 1's and 0's are going thru , eventually I'm going to run out of bits.


I don't want to zero all bits , because I still need the results behind.


Example

000010000000001000000001000001000000100100000

^ < < < < < < < Wrap Around < < < < < < < <
Beginning__________________________Dump Gate

My question is , how do I wrap around to the very first bit with new results , but keep the results that were coming behind going to the Dump Gate ?



Thanks so much in adavance

I'm sorry . This is going to be a SLC 500 PLC. ( RS Logix 500 )

Are you saying you will have more than 300 parts between beginning and dumpgate?

I'm sorry guys . I think I have it .


Thanks , Just a Monday morning mistake.

We need a bit more information for example: why do you need to wrap around ?
If there is a dump gate then the only reason is that this is a circular conveyor so should a part not dump it will eventually go round again.
There are a number of things that need to be considered. Assume the "circular" conveyor is effectively 350 bits long then the dump gate is at 300 a bad part is not dumped then when a bad part reaches 350 you will need to insert it into bit 0.
Without knowing exactly what your system consists of then we can only make assumptions. so here goes.
A part arrives before the conveyor (good or bad) you need to detect if there is a part still on it's way because it's missed so you have to hold the part back to allow the one on the "circular" conveyor" to go around again and insert this into the good/bad variable that populates the FIFO. without a good explanation of your system we can only guess.
Here are some things to consider:
Is a bad (or good) part going to re-enter the entry point of the shift.
How many times is this part going to go round until some action needs taking.
What takes the good parts off.
Where are these taken off.
Is it possible to detect a part going back onto the FIFO (good or bad).
etc. etc.
Some years ago I did a Pick & place system with about 15 stations. this consisted of a rotating table with P&P stations located around it. A base part was placed in a nest on the table it then was indexed to the next station. a part was inserted into the base & it then rotated. a checking station ensured the insert had been placed in the base part, this then indexed to the next station so in essence parts were placed in order, checked then removed. so essentially there were parts inserted, checked, removed (2 stations one for good one for bad), this contained a complex shift as we needed to track if a base part was inserted, if a component was inserted and if a good or bad part was removed. If a good/bad part was not removed after 3 rotations then the system would stop. so you can see there was a lot of information being tracked round the system if no part or a bad part was detected then the other stations would not insert it's own part.
This is the sort of information we really need. Take a look at some recent posts there have been a number of posts regarding shift registers although none of these catered for re-insertion.