PySerial and IronPython - get strange error

Question

I have a device connected to COM31. And the code that I need to create a serial connection looks very simple

port = 31
trex_serial = serial.Serial(port - 1, baudrate=19200, stopbits=serial.STOPBITS_ONE, timeout=1)

The foollowing code works when I run it using Python2.6, but when executed by IronPython2.6.1, this is what I get:

Traceback (most recent call last):
  File "c:\Python26\lib\site-packages\serial\serialutil.py", line 188, in __init__

  File "c:\Python26\lib\site-packages\serial\serialutil.py", line 236, in setPort

  File "c:\Python26\lib\site-packages\serial\serialcli.py", line 139, in makeDeviceName

  File "c:\Python26\lib\site-packages\serial\serialcli.py", line 17, in device

IndexError: index out of range: 30

I am not sure what is going on. PySerial clearly says that it is IronPython compliant. Any ideas what am I doing wrong?

Answer 1

IronPython is asking .NET what the ports are. They are enumerated differently. Most likely you are asking to open a connection that doesn't exist as far as IronPython/.NET is concerned. To find out the "real" port number, use the following code modified from the pySerial scan examples. Then use the number next to the listed COM.

import serial

def scan():
#scan for available ports. return a list of tuples (num, name)
available = []
for i in range(256):
    try:
        s = serial.Serial(i)
        available.append( (i, s.portstr))
        s.close()   # explicit close 'cause of delayed GC in java
    except serial.SerialException:
        pass
    #You must add this check, otherwise the scan won't complete
    except IndexError as Error:
        pass

for n,s in available:
    print "(%d) %s" % (n,s)

return available

The output looks like this for me:

(0) COM9

(1) COM15

(2) COM16

(3) COM1

(4) COM15

Then when you try to open the connection, use the number on the left NOT the actual COMportNumber - 1. For instance I need to open a connection to COM15, so using the above scan:

def IOCardConnect():
try:
    connection = serial.Serial(4, 115200, timeout=1, parity=serial.PARITY_NONE)
    print "Connection Succesful"
    return connection
except serial.SerialException as Error:
    print Error

Also, once you are connected, pySerial will expect bytes to write to the connectio, not strings. So make sure you send like this:

#Use the built in bytes function to convert to a bytes array.
connection.write(bytes('Data_To_Send'))