CSCI E-93: Application Note 7

Notes on Using Serial Port I/O
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o In a string constant in C, the \n (new-line) escape character is
  mapped to a line-feed (0x0a) character.

o In a string constant in C, the \r (carriage-return) escape character
  is mapped to a carriage-return (0x0d) character.

o Input of the Enter key: When the Enter key is pressed in a terminal
  emulation program, a carriage-return (0x0d) is sent to the UART.  On
  old keyboards, this key was originally labeled as "return."

o Input echoing: By default, characters typed in a terminal emulation
  program are *not* displayed.  Your assembly language code should be
  responsible for echoing the character back to the terminal emulation
  program if you want it to be displayed.  This allows some input to
  be displayed and other to not be displayed (for example, when a
  password is typed).  You could decide to implement a serial port
  attribute in your assembly code that would determine whether input
  characters are echoed back to the source.

o Input echo in SecureCRT and PuTTY: In SecureCRT and PuTTY, there is
  a mode that would display all characters when typed -- it is "Local
  echo" (in Advanced Emulation in SecureCRT).  We suggest that you do
  *not* turn on "Local echo."

o Output of carriage-return: When a carriage-return (0x0d) is output
  to a terminal emulation program, the cursor moves to the beginning
  of the current line (but does not move to the next line).

o Output of line-feed: When a line-feed (0x0a) is output to a terminal
  emulation program, the cursor moves to the same position on the next
  line (but does not move to the beginning of the line).

o Output to go to the beginning of the next line: You should
  explicitly first send a carriage-return then a line-feed to go to
  the beginning of the next line.  If you decide to implement serial
  port attributes in your assembly language code, then you could have
  a serial port attribute that would determine whether outputting a
  line-feed (new-line) would actually output a carriage-return
  followed by a line-feed or just a line-feed.

o Carriage-return and line-feed behavior in SecureCRT: We suggest that
  you do *not* turn on "Translate incoming CR to CR/LF" mode under
  Advanced Emulation.  This would affect how CR is displayed when
  received by the terminal emulation program.  "Translate incoming CR
  to CR/LF" would display both a CR and LF whenever a CR was received
  by SecureCRT.

o Carriage-return and line-feed behavior in PuTTY: We suggest that you
  do *not* turn on either "Implicit CR in every LF" and/or "Implicit
  LF in every CR" modes.  These would affect how characters are
  displayed when received by the terminal emulation program.
  "Implicit CR in every LF" would display both a CR and LF whenever an
  LF was received by PuTTY.  "Implicit LF in every CR" would display
  both a CR and LF whenever a CR was received by PuTTY.

o Typing a backspace (BS) or delete (DEL) in SecureCRT: As expected
  (and by default), when connected to a serial port, SecureCRT will
  send a backspace (BS) character (0x08) when the backspace key is
  typed and will send a delete (DEL) character (0x7f) when the delete
  key is typed.  See the SecureCRT "Options -> Session Options"
  "Terminal -> Emulation -> Mapped Keys" to change this behavior.

o Typing a backspace (BS) in PuTTY: By default, when connected to a
  serial port, PuTTY will send a delete (DEL) character (0x7f) when
  the backspace key is typed rather than sending the backspace
  character (0x08).  See the PuTTY "Keyboard configuration panel" to
  change this behavior.  Typing shift-backspace will cause PuTTY to
  send whichever code isn't configured as the default.

o PuTTY's action on receiving a delete (DEL): Normally, when PuTTY
  receives a delete (DEL) character (0x7f) to be displayed, it will
  perform a "destructive backspace" (i.e., it will move the cursor one
  space left and delete the character under it).  See the PuTTY
  "Features Panel" to configure the delete (DEL) character to perform
  a normal backspace (without deleting a character) instead.