Paul__B:
Well, that is what it is for, and its crucial and in fact, only purpose.
I disagree - it would be used for whatever a designer building the chip into a circuit would want,in the same way as a programmer using the shift instruction in a piece of software would use the overflow/remainder bit. And knowing how the chip behaves is the crucial thing.
Well, you can disagree all you want. 
Yeah, the designer can use it how he likes. But if you use the Q7' for something other then daisy chaining I thing the designers of the chip will call that misusing it 
Well, I solved the problem of the overflow pin being unaffected by the OE.
Simply added a transistor NOT gate ..
Base - picked up from the supply to the OE (Pin 13) which is held High until I'm ready during Setup().I have a resistor and LED in this part of the circuit.
Collector is from the Q7' (overflow pin 9 on the shift register), with the resistor and LED to suit
Emitter to earth.
Both LED's are restricted to 5ma
The transistor I used to get it working was a 2N3904.
The basic NOT gate circuit filched from my copy of "Electronics for Dummies" - available online at <b>Electronics Projects: How to Create a Transistor NOT Gate Circuit</b> - dummies
The use of an LED on both paths means I have indication of when overflow is triggered, and also a visual indication of the startup phase of my application.
So I've worked out how to solve the problem, in case anyone wants to do something similar. At some point I'll produce a schematic and some notes to pop into an appropriate part of the forum, when I've found out where.
But new trouble, that does not work push pull 
septillion:
But new trouble, that does not work push pull
Not sure what that means, or whether its relevant in my context (learning the behaviour of the overflow output and how to control it)
In your application, probably not. But in general, yes, because with your solution Q7' behaviors different from the rest.
The normal outputs are able to source (drive high) but also sink (drive low). If you add a single resistor you can only do one of those (depending on the type of transistor).
RMurphy195:
Well, I solved the problem of the overflow pin being unaffected by the OE.Simply added a transistor NOT gate ..
Base - picked up from the supply to the OE (Pin 13) which is held High until I'm ready during Setup().I have a resistor and LED in this part of the circuit.
Collector is from the Q7' (overflow pin 9 on the shift register), with the resistor and LED to suit
Emitter to earth.
Both LED's are restricted to 5ma
The transistor I used to get it working was a 2N3904.
The basic NOT gate circuit filched from my copy of "Electronics for Dummies" - available online at <b>Electronics Projects: How to Create a Transistor NOT Gate Circuit</b> - dummies
The use of an LED on both paths means I have indication of when overflow is triggered, and also a visual indication of the startup phase of my application.
So I've worked out how to solve the problem, in case anyone wants to do something similar. At some point I'll produce a schematic and some notes to pop into an appropriate part of the forum, when I've found out where.
Hello RMurphy !
I have the exact same issue as yours and I tried your solution with a transistor but I can't get it work perfectly. I think I miswired it. Would you have a schema or a picture of the wiring to share ? It would be great !