Hi Walter,

Thanks for the help. I'm going to have to work on this in the background unfortunately because of a sudden unexpected pile of work which has just descended (meaning from Above, if you know what I mean!) onto me. I'll get back to you as soon as I can clear some of the work and have some news. Thanks also for the link to your previous effort, very informative.

Thanks Acetronics for the pointer - I'll take a look but I think it best for my education to persist with the asm challenge as no doubt there will be other times when I will need to do something similar with asm code I come across.

Kind regards to all.
Bill