- DB9 RS232 RS422 RS485
  1 DCD T- = A+ DATA- = A+
  2 RX T+ = B- DATA+ = B-
  3 TX R+ = A+ -
  4 DTR R- = B- -
  5 GND GND GND
  6 DSR RTS- -
  7 RTS RTS+ -
  8 CTS CTS+ -
  9 RI CTS- -
  10 - - -

sticker DB9 connector

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ref