Internet PLC Forum

General => Technical support => Topic started by: garysdickinson on March 11, 2013, 12:10:37 AM

Title: Full Duplex RS-232 for Nano-10
Post by: garysdickinson on March 11, 2013, 12:10:37 AM

I have had a need to support full duplex RS-232 with the Nano-10.

As you are aware the Nano-10's serial interface is RS-485 (half duplex) which can be translated to RS-232 signal levels with TRi's "Auto-485".  Unfortunately the "Auto-485" can only support half duplex on the RS-232 side.  Half duplex means that serial data can not be sent and received simultaneously.

There are many RS-232 devices that do not work well with half duplex communications.  I have found that the Nano-10's serial interface and firmware can support full duplex communications.

I've attached a file that documents how I converted the Nano-10 to full duplex RS-232 for about $4.00 USD.

Please be aware that what I did is something that TRi will not endorse and you run a chance of destroying your Nano-10.

You have been warned.

Gary D

Title: Re:Full Duplex RS-232 for Nano-10
Post by: BC SYSTEMS on March 25, 2013, 07:58:45 AM

Hi Gary,

Great document. Thanks.

Marcus

Title: Re:Full Duplex RS-232 for Nano-10
Post by: garysdickinson on March 25, 2013, 11:56:46 AM

Thanks Marcus,

I was thinking of you when I wrote this up.  Your projects seem to revolve around connecting very unusually things to the PLCs.

One thing I forgot to mention, is that the cheap TTL to RS232 level converter that I used does not drive any of the handshake lines (DSR ...).  The TRi PLCs usually drive a single pin at about +9V and this signal is usually DSR, data set ready.  TRi PLCs don't pay any attention to the handshake signals from the other device nor does the PLC ever de-assert the handshake signal that it does provide.

This may have some effect on cabling.  Some external devices need to see an asserted signal before these devices are happy. If your cabling used the signal on the PLC end of the serial cable to drive the handshake signal on other end of the cable, you may need to adjust your cabling.

There are many of these TTL to RS232 level converters on the market. Many of them have jumpers that would provide greater flexibility.

The level converter that I used has no jumpers. The standard TTL / rs232 converter chip used on the board, does have an unused RS232 driver that could probably be used to drive a handshake line.  

Best regards,

Gary d

Title: Re:Full Duplex RS-232 for Nano-10
Post by: support on March 28, 2013, 04:09:14 PM

Thanks Gary for the suggestions. It should benefit some users. However, since the user is dealing with the 5V TTL directly it is possible that a wrong connection could kill the CPU - which is typically not repairable. So it is a case of user-beware :).