Control codes are the first 32 characters in the ascii character set that may have meaning to the printer or terminal but don't print. CR/LF/FF are 3 of them that are used on every print job.
You can put control codes in the interface scripts to do all sorts of things. For example, I had a PC as a terminal that needed to use an attached printer in an emulation that didn't handle passthru printing natively. So prior to the cat statement in the printer script I used an echo statement that forwarded the control codes to turn the keyboard off, turn the terminal off, turn the printer on, tell the printer how to print, then cat the file, then reverse the steps to bring the terminal and printer back to normal operation.
I've run across the 7 bit, but it was a long time ago. Think I used stty to convert how the printer used it by defining the port but it is in the dim past.
Might try man ascii or man stty. Ed Fair
efair@atlnet.com
Any advice I give is my best judgement based on my interpretation of the facts you supply.
Help increase my knowledge by providing some feedback, good or bad, on any advice I have given.