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USB keyboard in Point of Sale.
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Module to connect an additional usb keyboard for Point of Sale.
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The processed keys:
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1. numChar: 0-9, '.'
2. mode: 
* qty: '/'[1]_ or "q"[2]_    
* disc: '-'[1]_ or 'd'[2]_
* price: '*'[1]_ or 'p'[2]_
3. backspace: 'backspace'
4. +/-: '+'[1]  or 's'[2]_

[1]_ key on additional keyboard
[2]_ key on basic keyboard