[GreenKeys] TTY protocol

[Sam Hallas]

Dave Meier wrote:
>  I found a wikipedia entry which explained this.  It also said that
>  the NNNN punched hole pattern was just a series single hole punches
>  to be easily identifiable to the operator as the tear point.

Dave, I couldn't find the article. Could you post the link, please?

I have a feeling that the use of ZCZC & NNNN predates WWII and most 
likely started with the cable operators like Cable & Wireless, where 
torn tape relay was widely used.

Cheers,
Sam