fixes for RTS/DTR handling on open (#59)

- internal RTS/DTR state defaults to None
- serialwin32 and serialcli platforms override that to True (as before)
- serialposix leaves it unset and therefore does not touch RTS/DTR on open
  (as it was in pySerial 2.7 and before)

1 files changed, 5 insertions, 0 deletions

diff --git a/serial/serialwin32.py b/serial/serialwin32.py
index 658f13f..9e300e1 100644
--- a/serial/serialwin32.py
+++ b/serial/serialwin32.py
@@ -39,6 +39,11 @@ class Serial(SerialBase):
             raise SerialException("Port must be configured before it can be used.")
         if self.is_open:
             raise SerialException("Port is already open.")
+        # if RTS and/or DTR are not set before open, they default to True
+        if self._rts_state is None:
+            self._rts_state = True
+        if self._dtr_state is None:
+            self._dtr_state = True
         # the "\\.\COMx" format is required for devices other than COM1-COM8
         # not all versions of windows seem to support this properly
         # so that the first few ports are used with the DOS device name