CSCI E-92: Application Note 16

Notes on Using Serial Port I/O through a UART
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Configuring the serial port:

o In SecureCRT, setting the Port name, the serial communication Baud
  rate (i.e., the number of bits per second), the number of Data bits,
  whether Parity is enabled, the number of Stop bits, and whether Flow
  control is enabled, are accomplished in "Connection -> Serial."
  These should be set as follows: Port as reported by the host OS,
  Baud rate as configured in the K70, Data bits to 8, Parity to None,
  Stop bits to 1, all Flow control (DTR/DSR, RTS/CTS, XON/XOFF) *not*
  checked.

o In PuTTY, setting the Port name, the serial communication Baud rate
  (i.e., the number of bits per second), the number of Data bits,
  whether Parity is enabled, the number of Stop bits, and whether Flow
  control is enabled, are accomplished in "Connection -> Serial."
  These should be set as follows: Serial line to connect to as
  reported by the host OS, Speed (baud) as configured in the K70, Data
  bits to 8, Stop bits to 1, Parity to None, Flow control to None.

Line termination character handling:

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."

Input echoing:

o By default, characters typed in a terminal emulation program are
  *not* displayed.  The OS you are developing will be responsible for
  echoing each 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).
  If you decide to implement serial port attributes in your OS, then
  you could have a serial port attribute in your OS that would
  determine whether input characters are echoed back to the source.  A
  mode that displays all characters when typed is referred to as
  "local echo".

o In SecureCRT, local echo is controlled under Terminal -> Emulation
  -> Advanced, do *not* check "Local echo."

o In PuTTY: local echo is controlled under Terminal in the "Line
  discipline options" section.  For"Local echo:" select "Force off."

Handling of carriage-return and line-feed characters:

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: In your OS, 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 OS, then you could have a serial port
  attribute in your OS 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 In SecureCRT, set Carriage-return and line-feed behavior as follows.
  Do *not* turn on "Translate incoming CR to CR/LF" mode under
  Terminal -> Emulation -> Advanced.  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 In PuTTY, set Carriage-return and line-feed behavior as follows.  Do
  *not* check "Implicit CR in every LF".  Do *not* check "Implicit LF
  in every CR".  These modes 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.  These options are found in
  PuTTY under Terminal.

Handling of BS (backspace) and DEL (delete) characters:

o In SecureCRT, set the behavior for typing a backspace (BS) or delete
  (DEL) as follows.  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 In PuTTY, set the behavior for typing a backspace (BS) as follows.
  By default, when connected to a serial port, PuTTY will send a
  delete (DEL) character (Control-?, 0x7f, 127) when the backspace key
  is typed rather than sending the backspace character (0x08).  You
  should modify the character sent by typing the backspace key from
  "Control-? (127)" to "Control-H."  The option to change this
  behavior is under Terminal -> Keyboard.  Typing shift-backspace will
  cause PuTTY to send whichever code isn't configured as the default.
  PuTTY should send a delete (DEL) whenever the delete key is typed.

o In PuTTY, set the behavior on *receiving* a delete (DEL) as follows.
  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 "Terminal -> Features" to configure the delete (DEL)
  character to perform a normal backspace (without deleting a
  character) instead by checking "Disable destructive backspace on
  server sending ^?," if desired.