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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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number: 0-9
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mode: 
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 qty: '/'* or "q"**
 disc: '-'* or 'd'**
 price: '*'* or 'p'**
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dot: '.'
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backspace: 'backspace'
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+/-: '+'*  or 's'**
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* key on additional keyboard
** key on basic keyboard
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