
RS-232C 
Pin  | I/O  | Symbol  | Description  | 
  | In the UPS  | 
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  | ||||
1  | 
  | This pin not used  | 
  | N/C  | 
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  | 1  | ||||
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2  | Input  | RXD  | Receive Data  | 
  | RXD  | 
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  | 2  | ||
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3  | Output  | TXD  | Transmit Data  | 
  | TXD  | 
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  | 3  | ||
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  | 4  | 
4  | Output  | DTR*  | Data Terminal Ready  | 
  | 
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  | ||
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  | |||||
  | GND  | 
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  | 5  | |||||||
5  | -  | GND  | Signal ground  | 
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6  | Input  | DSR*  | Data Set Ready  | 
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  | 6  | |
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7  | Output  | RTS**  | Request to Send  | 
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  | 7  | 
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8  | Input  | CTS** | Clear to Send  | 
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  | 8  | 
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9  | 
  | This pin not used  | 
  | N/C  | 
  | 
  | 9  | ||||
  | 
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  | |||||||||
(*)(**) These pins are tied together internally in the UPS. Signals DTR, DSR, RTS, and CTS are not used.
DB9 Female Connector Outline (facing connector)
1800 Series User Manual  | 27  |