Jump to content

Comm Config Parity Glitch


Recommended Posts

For some reason, the CommInit Function block will not allow me to select Parity as "None" with 7 Data Bits. Why not? I can with hyperterminal. And the device I am trying to talk to is set up with these settings.

If you try and select NONE, it just ignores you and puts back in EVEN parity. I found this after a couple hours of scratching my head, because I assumed that it was actually using the settings I selected.

If you try to out smart it, and select 8 data bits first, then no parity, and then go back and change the data bits back to seven, it immediately stuffs an even back in the Parity.

Can this be fixed?

Link to comment
Share on other sites

Hi Damian,

According to the standard, the "word" in RS232/485 needs ot be 10 or 11 bits. You always have one start bit. Then you wnt to set 7 data bits, no parity and one stop bit. The result is 9 - not standard! That's why COM Init module doesn't let you to chose this combination.

Link to comment
Share on other sites

Hi Damian,

According to the standard, the "word" in RS232/485 needs ot be 10 or 11 bits. You always have one start bit. Then you wnt to set 7 data bits, no parity and one stop bit. The result is 9 - not standard! That's why COM Init module doesn't let you to chose this combination.

Hi Emil,

Can you please point me to where in the standard this is supposed to be? RS232/485 as far as I know is an electrical standard that does not dictate any protocol. I think you are maybe thinking of Modbus Ascii, in which case your above statement rings true.

You have given me the freedom, using the Protocol function blocks, to accomodate non-standard protocols. Making it so that I can't select different combinations of communication parameters takes some of that freedom away.

Thanks,

D

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

×
×
  • Create New...